Round-Trip Angel Island: A Devil of a Swim

If I had to nominate a single, definitive marathon swim of San Francisco Bay, it would be the Round-Trip Angel Island.

Start at Aquatic Park’s “swimmers’ beach” between the South End and Dolphin clubs, swim out into the Bay, past Alcatraz to Angel Island (3.5 miles), around the island (3 miles), and then back to Aquatic Park (3.5 miles). Ten “honest” miles by shortest route, mostly perpendicular to the tidal flow.

Round-Trip Angel Island route
Round-Trip Angel Island route

Angel Island is the second largest island inside the Bay (behind Alameda), and has functioned at various times through history as a military fort, an immigration station (like a west coast Ellis Island), and currently as a California State Park.

angel island
Angel Island from the air. Yerba Buena and Treasure Islands, Bay Bridge, San Francisco city skyline, and Alcatraz visible in background.

The Round-Trip Angel Island (RTAI) is like the Round-Trip Alcatraz (RTA)…squared — almost literally, by distance. The 3.2-mile Round-Trip Alcatraz is an annual South End club swim — and Water World Swim organizes a popular public version called the “Swim Around the Rock.” A RTAI swim involves many of the same features and challenges as a RTA: scenic views, iconic landmarks, complicated currents, and busy shipping channels — requiring skill from both the pilot and swimmer. But the RTAI is three times the distance – a true marathon swim by any measure.

According to the best word-of-mouth history I could obtain, the Round-Trip Angel Island swim was pioneered by South End member Rick Barthels (first American to complete the Triple Crown) in August 1995. The swim has been replicated by only five swimmers since: Tom Linthicum (July 2009), Mike Tzortzis (August 2009), Hendrik Meerman (August 2011), Cathy Delneo (August 2013), and Delia Salomon (May 2015).

I compiled the following list of successful Round-Trip Angel Island solo swims, understood to have been completed nonstop, without being re-positioned, and according to traditional marathon swimming rules. Details included as available.

If anyone reading this is aware of other successful, nonstop, non-repositioned, traditional-rules RTAI swims, please contact me via this form.

1. Rick Barthels

August 8, 1995. 6 hours, 39 minutes.

[via personal communication]

Date Aug. 8, 1995, jump 4:08 am, finish 10:47 am., elapsed time 6hr 39min +/-. Conditions starting out were flat, no wind, course was clockwise from the club to the west end of Angel Island, passing Alcatraz to the west, visibility incredibly clear, water very comfortable at around 62 degrees, feedings consisted of Cytomax every 15-20 minutes. Pilots were Andy Field on kayak, Bob Roper and Mike Laramie in the avon. Somewhere approaching Pt. Blunt on Angel Island course was set toward Treasure Island/Bay Bridge to compensate for an ebb. Spent about 45 minutes swimming in place between Angel Island and the east end of Alcatraz, not sure why but I finally broke loose and headed toward the Ferry Building and caught the increasing ebb tide.

Tom Linthicum (first attempt, DNF)

June 18, 2009.

[via South End mailing list]

This morning I met the Sunrisers who were going to swim to Fort Mason. I felt low as I saw them get into the water and thought how come I could not be a normal swimmer? I was getting ready to swim a Club to club Round Trip Angel Island Swim! Bill James was my pilot. Tina and Susan greeted me just before I jumped and help get my Reptile Brain in gear as I went in backwards (7:12 AM) like I did in Tahoe.

Roper and Paddy Payton helped my plan the tide. Roper said I would have to fight the flood all the way to Angel Island then hopefully get a push to the north tip of the island near Ayala Cove (11:22 AM). It took me an hour to get past Alcatraz that was on my right side for a long time. Then I made it to the green Buoy (8:12 am). Then I was pushed east and Alcatraz was on my left for a long time finally we seemed to be making progress to Angel Island. It took a long time to make it past the first point on Angel Island. The water was warm 61 degrees! At times I was not real happy then I discovered if you close one eye 1/2 of the brain does not even know you are swimming. Then I started randomly counting strokes up to 1000. The water smoothed out and the Sun was warm as I rounded Ayala Cove. I put headed away from the island to be ready for the ebb as I headed South. It is really fun to look at Angel Island as you swim by!

Bill was amazing! I told him I had a leg cramp and he said I can’t do anything about that! LOL. I think I did too much running this week so my legs were not really swim ready! I got into a good zone as I progressed South. I hung up near Point Blunt and because of the fog could not really see where we were going. The wind picked up and white caps were all around me! I could see the North tower and eventually we slipped into the rough water farther South. It felt like a Water Massage. I was drinking a lot of Bay water!

At my last feeding at about 6 hours into the swim Bill said its getting too rough. Do you want to quit? I said no! About 15 min later Bill came over and said I’m calling the swim its over get in the Boat. I did not argue because I could see he was having trouble keeping the boat on course so I really was not sure where to go. I could only see the East Bay hills and the North Tower. I felt pretty good and was keeping in a good mental zone and I thing the waves were helping my sore muscles. Bill did a great call and if he had not pulled me I think I would still be out there!

Thanks Bill, Paddy, Roper, Susan, Tina and everyone else who sent me good energy during the swim! Jon Meyer was about to send out a rescue because he could see how rough it was getting!

Rick Barthels is the only one who has ever been able to complete this swim!

2. Tom Linthicum

July 14, 2009. 10 hours, 2 minutes.

[via South End mailing list]

From the desk of Bob Roper: “Proof the reptile mind exists!”

The reptile really came out of its shell this morning: coming back from South Lake Tahoe, Tom swam a ROUND TRIP ANGEL ISLAND, in the phenomenal time of 10 hours, 2 minutes!

Starting out at 3AM at the shores of the South End Rowing Club, Tom (piloted by Bob Roper and Warren Wilson, in Warren’s “Tricaps”) swam to the east end of Alcatraz, and there to the west end of Angel Island. There he encountered the start of the ebb tide: he battled for almost two hours to get around the northeast of the island. He shot past Pt. Blount, and then encountered 3-to-4 foot waves! He made it 3/4 of the way to Alcatraz before getting caught in the back eddy off Alcatraz. But, by his sheer tenacity and NUTCRACKER upbringing he defeated Mother Nature and broke loose from Father Neptune’s grasp. After turning the corner at the east end of Alcatraz, he experienced the start of the flood: with the wind and the tide, Reptile was pushed down to Pier 41! (I was sure then that Tommy would throw in the towel!) He battled the increasing winds and tides and swam into the into the breakwater to the South End beach! Surely into the arms of 72 virgins!

At the end of the swim I asked Warren what he thought of tom’s Herculean effort, Warren just shook his head and said “F—g insanity!”

Tom will go down in Bay swimming infamy as the 2nd person ever to do this swim (his after a brave Tahoe attempt!): truly an exceptional feat! After he completed the swim, Tom passed up a shower and sauna and laid back in his viper car to regenerate his reptile brain! This goes to prove forever that there truly is a reptile mind!

3. Mike Tzortzis

August 29, 2009. 6 hours, 49 minutes.

[via South End mailing list]

It was a great swim under really perfect conditions, except maybe the windswept, mean choppy, final crossing from Alcatraz to the Club (“it’s just an Alcatraz…” I had to keep telling myself).  Rick Russel, a friend of mine did a great job of piloting in in his trusty little Zodiac, negotiating our way across the various shipping channels with constant contact with VTS and the captains. Tides were right and a shout out to Paul Saab  in Europe for pointing me to this date on tide calendar.

4. Hendrik Meerman

August 23, 2011. 4 hours, 46 minutes.

Report from pilot BJ James [via South End mailing list]

Hendrik Meerman started swimming from SERC at 4:00 AM to swim around Angel Island and back to Aquatic Park.  He finished at the club at 8:46 AM.  Mike Tzortzis expertly guided him from a Kayak and Irene Chan ensured that he was given timely feedings so that he could continue swimming at an amazing pace.  The winds were very light.  The biggest concern was the fog.  We had to navigate by compass from Pt Blunt to Alcatraz.  It was a great adventure.

meerman angel island
GPS track of Hendrik Meerman’s Round Trip Angel Island swim

5. Cathy Delneo

August 30, 2013. 6 hours, 10 minutes.

Piloted by Paul Saab in the inflatable “Big Red.” Observed by Evan Morrison.

Cathy entered the water from the South End beach at 4:10am, just after slack at the Golden Gate. It was quite dark, with patchy fog obscuring what little illumination the quarter-moon offered. Paul deftly piloted us past Alcatraz and toward Pt Stuart. Cathy made good progress with little resistance from the building flood, and we reached the mouth of the Raccoon Strait in 2 hours, 10 minutes. The flood swept us through the Strait and we reached the top of the island at 6:50am.

Swimming down the east side of the island in the lee of the wind, the Bay waters were breathtakingly glassy, reflecting the glow of the pre-sunrise. We passed Pt Blunt at 8:10am and were immediately pushed east by the flood. We crabbed back toward Alcatraz as the sun rose on a gorgeous San Francisco morning.

The wind picked up a little as we passed Alcatraz, and we remained watchful for approaching boat traffic. Cathy continued making good progress despite the wind chop. The current seemed to switch about halfway across the south shipping channel, sweeping us back toward Aquatic Park just in time to deposit Cathy along the breakwater. She turned the corner into the cove, and cleared the water at 10:20am as the first woman to complete the RTAI.

delneo rt angel island
GPS track of Cathy Delneo’s Round-Trip Angel Island swim.


6. Delia Salomon

May 22, 2015.

Awaiting details – check back soon.

[Updated 7/12/2015]

7. Evan Morrison

July 12, 2015.

5 hours, 57 minutes. Report forthcoming.

* The clever title is courtesy of Tom “Reptile” Linthicum.


Standardized Swims and Routes

As previously defined, a swim route is a predetermined, abstract path between a start location and a finish location, composed of a straight line or series of connected straight-line segments.

Let’s further define a standard swim route as an established, recognized route used by most (or all) attempts of a given swim. A standard route is established either informally, through a history of successful swims along the route; or formally, by a sanctioning organization.

Finally, let’s define a standardized swim as a swim for which a standard route has been established.

Most well-known marathon swims are standardized swims, with standard routes:

  • An English Channel swim, by default, covers the straight-line route between Dover and Cap Gris Nez.
  • A Catalina Channel swim, by default, covers the straight-line route between Doctor’s Cove/Arrow Point and Point Vicente.
  • A Boston Light Swim starts at Little Brewster Island and finishes at the L Street Bathhouse, via a meandering route among several islands in Boston Harbor.

Why does this matter? Consider the following hypothetical:

Perhaps I’m not satisfied with the typical English Channel route — I want to be different and special and do something no one’s ever done before. Perhaps I’ll start at Dungeness instead of Dover (adding ~6 miles to the total swim distance)!

How does the sanctioning organization (CS&PF or CSA) treat this swim, if it’s successful? Should it be recognized as a “first”? Or is it the same as any other English Channel swim (anywhere on the English shore to anywhere on the French shore)?

It is the sanctioning organization’s prerogative to recognize (or not recognize) more than one standard swim route. The English Channel and Catalina Channel organizations currently do not recognize multiple routes. Jim Fitzpatrick once finished a Catalina Channel swim at Newport Beach (~9 miles longer than the standard route), but it is recognized the same as all other Catalina-mainland swims.

Standard swim routes simplify matters for both the swimmer and the sanctioning organization.

  • If there’s no recognition to be gained from a different route, most swimmers will simply choose the default.
  • As more “standard route” swims are attempted, more knowledge is gained about the route, thus helping future swimmers.
  • Swims along a single standard route are more comparable than swims along different routes.
  • A sanctioning organization can simply list a successful completion of the standard route, without having to note the precise start and finish locations of each swim.

How Standard Swim Routes Develop: A Case Study

Consider the history of swims across the length of Lake Tahoe.

The first known lengthwise swim was completed by Fred Rogers in 1955, between Kings Beach in the northwest and Bijou in the southeast — a 20 statute mile route.

rogers lake tahoe
Fred Rogers, first Lake Tahoe lengthwise swim. Kings Beach to Bijou.

However, most modern (post-2004) Lake Tahoe lengthwise swims have used a different route, approximately 1.25 miles longer, between Hyatt Beach near Incline Village in the northeast, and Camp Richardson in the southwest:

standard tahoe swim route
Standard lengthwise Lake Tahoe route: Camp Richardson to Hyatt Beach.

The first to complete the Camp Richardson / Incline route was Laura Colette, in 2004. Subsequently, almost every lengthwise Lake Tahoe attempt has used this same 21.25-mile route. This is quite remarkable, given there is currently no functioning sanctioning organization for Lake Tahoe swims.

I asked Laura why she chose this route, and she confirmed my intuition: Because this route (southwest / northeast) covers the longest axis of the lake. Why does that matter? Because there can be only one longest route across a lake, but an infinite number of shorter routes. Therefore, it is a natural candidate for a standard swim route.

Before Laura Colette, eight swimmers had successfully swum the length of Lake Tahoe — using eight different routes ranging from 16.8 to 21.0 miles.

After Laura swam the longest-possible route (21.25 statute miles) in 2004, all subsequent Tahoe lengthwise aspirants were faced with the choice of either replicating her route, or doing a shorter route and opening themselves to the potential criticism of not doing a “full” lengthwise swim. Even in the absence of a sanctioning organization, Laura’s route became the de-facto standard.

Issues in Selecting Standard Routes

In planning new or unprecedented swims, one of the most important and subtle challenges is defining an appropriate swim route.

The route used by a “first” swim may have precedence in defining a standard route, but this can be over-ridden if consensus subsequently develops for a different route (as demonstrated in the Lake Tahoe case study).

Standard swim routes are usually simple and obvious.

  • For a lake swim, there is only one longest route, but an infinite number shorter routes. If the longest route is a swimmable distance, it is usually a natural candidate for the standard.
  • For a channel swim, there is only one shortest route, but an infinite number of longer routes. In this case, the shortest route is usually the natural candidate for the standard.

Standard swim routes define a minimum distance for a swim.

If the minimum distance is enforced by geography, the specific start and finish locations are less important.

Example: It’s impossible to swim a shorter English Channel swim than 20.5 miles. Even if an English Channel swimmer misses the Cap and finishes at Wissant or Aubresselles, we know they swam at least 20.5 miles. There is no concern about “cheating” the distance by finishing at a nonstandard location.

If the minimum distance is not enforced by geography, it is essential to start and finish at the specified locations.

Example: if you start and finish a Lake Tahoe swim at any location other than the southwest corner (Camp Richardson / Baldwin Beach area) and the northeast corner (Incline Village), you probably will have swum less than the standard distance of 21.25 miles. To complete a “full” lengthwise swim, you must respect the standard start and finish locations.

If there are multiple standard routes for a body of water, they should be categorically distinct swims – in terms of distance, conditions, and/or currents.


  • Lake Tahoe length vs. Lake Tahoe width (a ~10-mile route used for the annual Trans Tahoe Relay).
  • Farallon Islands to Marin County mainland (Stewart Evans and Craig Lenning) vs. Farallon Islands to Golden Gate Bridge (Ted Erikson and Joe Locke).
  • Santa Cruz Island to Ventura County (David Yudovin, myself, and others) vs. Santa Cruz Island to Santa Barbara County (Ashby Harper, Kevin Murphy, and others).

“Categorically distinct” is somewhat subjective, of course, but if multiple standard routes are truly justified, it should be obvious.

An unstandardized swim is a swim for which a standard route has not yet been established. In the next article, I will consider some principles and best practices in defining routes for as-yet-unstandardized swims.

Also in this series:

Measuring Non-Straight-Line Swim Routes

In the previous article, I discussed the difference between a swim route and a swim track, and how the measured distance of a marathon swim is always the length of the route, not the length of the GPS track. To demonstrate this principle I contrasted the standard English Channel route (a 20.5 statute mile line between Dover and Cap Gris Nez) and a typical English Channel track (a swooping S-curve as the swimmer is pushed back and forth by the tides).

Aha!, you might say: Not every swim route is a straight line! What about an island circumnavigation? Or a swim down a curving river?

Let’s review the definition of “swim route” from the previous article (emphasis added):

A swim route is a predetermined, abstract path between the start and finish, composed of either a straight line or (if the straight-line path is interrupted by another land-mass) a series of connected straight-line segments.

So, by this definition, even a non-straight-line route can be understood as a “series of connected straight-line segments.” The key in measuring a non-straight-line route is knowing how to select the intermediate waypoints — the “nodes” connecting each line segment.

The underlying principle is to create the shortest swimmable route between the start and finish, using fixed land features to define the waypoints.

Waypoint-Selection Algorithm for Non-Straight-Line Swim Routes

  1. From the start or any intermediate waypoint, move in the general direction of the finish.
  2. Find the location where your route line encounters land and creates the longest possible line segment from the previous waypoint. Create a waypoint at that location.
  3. If the route line does not encounter any land and heads off “toward infinite sea” (this will happen at least twice, usually more, on an island circumnavigation) then create a waypoint at a location where the next point of land is “visible” via straight-line path.
  4. Repeat steps 1-3 until you reach the finish.

Let’s work through some examples.

Case Study: Santa Rosa Island circumnavigation

How would one measure the distance of a circumnavigation of Santa Rosa Island (one of the eight Channel Islands of California)? This is an actual problem I was tasked with a few years ago, when I produced official measurements for the 54 swim routes governed by the Santa Barbara Channel Swimming Association.

Applying the waypoint-selection algorithm, we find a route distance of 41.1 statute miles.

santa rosa island
Santa Rosa Island circumnavigation route. Click to enlarge.

For island circumnavigations, the shortest route will typically follow close to shore. Even if you opt to swim further out, you can’t “take credit” for a longer route!

Note, though, for islands with sharply defined points and coves, the shortest circumnavigation path will “cut across” the coves rather than follow the shoreline. To understand why, think about the triangle inequality theorem. For the northeast portion of the above route (between Carrington Point and Skunk Point) the route-line is nearly 2.5 miles offshore!

Case Study: Angel Island “Round Trip”

A “Round-Trip Angel Island” (RTAI) swim in San Francisco Bay starts at the South End/Dolphin Club beach, heads straight out past Alcatraz to Angel Island, then around Angel Island, then back past Alcatraz again and returning to the start. It is a challenging cross-current swim that can only be attempted on certain tides. In 2013, I observed Cathy Delneo become the first woman to complete an RTAI.

Using the waypoint-selection algorithm, I measure the shortest RTAI route at 9.99 statute miles — let’s call it 10. And for sure, it’s an honest 10 miles — Cathy finished in 6 hours, 10 minutes.

Round-Trip Angel Island route
Round-Trip Angel Island route

Note that from the Aquatic Park “Opening,” it’s an uninterrupted straight shot to either the east or west end of Angel Island. Here’s a zoom on the start/finish at Aquatic Park:

round trip angel island
Round-Trip Angel Island route: Aquatic Park focus

Then, going around Angel Island the route follows a typical circumnavigation course, but with the “bottom” cut out.

round trip angel island
Round-Trip Angel Island route: Angel Island focus

Case Study: 8 Bridges Hudson River Swim, Stage 4 — Newburgh-Beacon to Bear Mountain

What about river swims? I chose a particularly curvy stretch of the 8 Bridges Hudson River Swim – Newburgh-Beacon to Bear Mountain. 8 Bridges directors David Barra and Rondi Davies independently rate this stage at 15.0 statute miles — let’s see how my waypoint-selection algorithm fares…

newburgh beacon bridge to bear mountain bridge
8 Bridges, Stage 4 route

And… I get 15.0 miles exactly. Nice!

It’s worth noting again: The route depicted above doesn’t necessarily reflect the actual path swimmers would take (i.e., the track). In a river, the fastest currents are often found in the middle. But we measure the official distance of a swim with the route, not the track, in order to maintain consistency and repeatability across different attempts of the same swim.

Try it yourself — instructions for measuring a route on Google Maps

  1. Browse to
  2. Search and zoom into your location of interest.
  3. From the right-click menu, select “Measure distance.”
  4. Click your starting location.
  5. (If necessary) Click any intermediate waypoints.
  6. Click your finish location.
  7. The total distance will automatically display.

This article benefited from conversations with Andrew Malinak.

Swim Route vs. Swim Track

Sometimes basic principles need to be stated. This one is frequently confused, even by experienced open water swimmers.

A swim route is a predetermined, abstract path between the start and finish, composed of either a straight line or (if the straight-line path is interrupted by another land-mass) a series of connected straight-line segments.

For example, the route of an English Channel swim is the straight-line path between Dover, England and Cap Gris Nez, France (approximately 20.5 statute miles, typically rounded up to 21 by the CSA and CS&PF).

english channel route
English Channel ROUTE

A swim route is typically the shortest path between the start and finish, though in some cases a longer path may make more sense (if certain characteristics of the shortest path make it undesirable, e.g., adverse currents).

In contrast, a swim track is where you actually swam – including navigation error, tidal movements, and other variables that cause differences between the abstract/ideal path and the actual path. A swim track is typically recorded with a GPS device.

For example, here is the track of a slower English Channel swim: The swimmer is first pushed southwest from Dover by the ebb tide, then northeast by the flood, then southwest by another ebb, then northeast by another flood and into the French coast.

english channel track
English Channel TRACK

This swimmer obviously traveled much further than 20.5 statute miles — but that is irrelevant in measuring the distance of the swim! A one-way English Channel swim is 20.5 statute miles, regardless of whether the track is a big S-curve or a straight shot across like Trent Grimsey’s record swim. You don’t get to “take credit” for going off-route!

The distance of a marathon swim is the length of the route, not the length of the track.

Read the next article in this series:

Top 10 DNF excuses you never hear

Presenting the top 10 excuses for not finishing a marathon swim you never seem to hear….

10. Quite simply, I decided I didn’t want to swim anymore.

9. I lack persistence, and have a hard time finishing things I start.

8. I got sick — not because the waves were 10 feet high and thrashing me around, but because I drank too much the night before.

7. I am a really slow swimmer even when I’m fresh. When I get tired, I literally stop making progress in the water.

6. I stopped after the first leg of my planned/announced two-way, because the solid ground felt sooo good and I didn’t want to get back in the water.

5. Marathon swimming is stupid.

4. I was hopelessly naive, and didn’t have any idea what I was getting in to.

3. I had to poo, but was too embarrassed to do it in front of my crew.

2. I didn’t really care about finishing anyway — it was more about getting publicity and attention for myself for just attempting it.

1. I didn’t train enough.

Making Independent Swims “Count”

For standard marathon swims such as the English Channel, Santa Barbara Channel, or Catalina Channel, swimmers need not concern themselves with “proving” they did the swim. For these swims, the authenticity of a swimmer’s claim is supported by the legitimacy of the local sanctioning organization — legitimacy derived from the marathon swimming community’s trust in the organization’s leaders and procedures.

A legitimate local sanctioning organization provides trained observers to document swims and verify adherence to the organization’s published swim rules. Although it’s difficult to “prove” an event witnessed by few, many miles out to sea, any swim ratified by trusted organizations such as the CS&PF, SBCSA, or CCSF is generally accepted without question by the marathon swimming community. A swim log completed by the official observer is viewed as the only “proof” needed (though ironically, these logs are almost never made public, and in some cases are held quite tightly by the organization).

But what about swims for which there is no well-established sanctioning organization? How do you make a swim “count” in ungoverned waters, without a trusted sanctioning organization to back up your claims?

(The phrase “making it count” in reference to marathon swimming derives from an upcoming book by Dr. Karen Throsby.)

This isn’t a new problem, of course. Marathon swimmers have been undertaking adventurous, independent swims since the beginning — indeed, even Captain Webb’s crossing was an “independent” swim, as were all English Channel swims before the formation of the CSA in 1927.

For most of our sport’s murky history, independent swims have been informally vetted on the basis of personal reputation — e.g., a well-established record of accomplishment on standard, sanctioned swims. If Kevin Murphy or Lynne Cox or David Yudovin (RIP) did a swim in some far-off land, it was simply accepted as truth. Lynne Cox swam; therefore Lynne Cox swam. Because Lynne and Kevin and David are known, trusted quantities.

david yudovin
David Yudovin in Sumatra. Photo courtesy of

In fairness, I believe many of the higher-profile independent swims of the past were observed, though much original documentation has been lost to the ages, apart from brief mentions in Wind, Waves, and Sunburn.

But recently there has been a paradigm shift in the standards and practices of documenting independent marathon swims. The shift may have been inspired at some level by certain high-profile, highly-doubted swim claims. But more fundamentally, the shift was made possible by advances in handheld technology and electronic communication, and the existence of an organization — the Marathon Swimmers Federation — specifically formed to serve independent swimmers.

Through my role as official observer on the first two successful Farallon Islands solo swims since 1967, I’ve given much thought in the past year to the challenges and opportunities of documenting independent swims. My report on Craig Lenning’s swim, published in April last year, eventually led to seven MSF Documented Swims. Multi-dimensional, multimedia reports that have helped make independent marathon swims more transparent to the community and more accessible to the public.

As we embark on the second year of MSF Documented Swims, I’m excited to find out what adventures my fellow swimmers will dream up, and to vicariously experience these adventures through their documentation.

The warmest winter on record in San Francisco Bay

Here in San Francisco, the common sauna wisdom is that we just experienced one of the warmest winters in recent memory. The Dolphin Club’s Polar Bear Challenge was hardly challenging, and the South End’s “Dreaded 9th” of February swim was hardly dreaded.

Just how warm was it, though? I crunched the numbers from the NDBC, because, well, why not.

Here we see the last 15+ months of data from the Crissy Field station (FTPC1) inside San Francisco Bay, plotted in solid black. The dashed green, red, and blue lines show the long-term average, maxima, and minima for each day of the year, summarized over the eight years of available data from that station.

san francisco bay water temp

From July 2014 until just the past few days (early April 2015), Bay waters have been hovering 2-3 degrees (F) above the all-time highs (going back to 2006), and about 5 degrees above the long-term averages.

Eight years isn’t much data, unfortunately. Can we do better?

A bit: Lightstation 46026 – about two-thirds of the way out to the Farallones – has data going back to 1982. Almost 33 years of data! This is colder, hairier water than inside the Bay, but it’s as close as we’re going to get.

Here’s a similar chart for this much longer-term data set. Unfortunately, the water temp sensor at Station 46026 was out of commission for the first eight months of 2014, so we can compare “recent data” starting from late August.

san francisco bay water temp

The story is similar, though: This was one of the warmest winters on record. Through most of December, we were ~4 degrees above the all-time highs going back over 30 years.

Indeed, when I took the average sea temps for each full winter season (December 1 through February 28), I found the following five warmest winters since 1982-83:

  • 2014-15     57.3 (F)
  • 2004-05     55.0
  • 2002-03     54.7
  • 1982-83     54.6
  • 1983-84     54.3

Only time will tell if the recent drop in Bay temps is a momentary aberration, or a longer-term regression to the mean.

No doubt, this summer’s Farallon swimmers will be watching this closely. 2014 saw the first two Farallon solos since 1967 — Craig Lenning and Joe Locke. And from a water temp perspective, 2014 was probably the best year to swim the Farallons in over a generation. We won’t always be so fortunate.

Data crunched with R and plotted with ggplot2.