On 9/17/2017 I raced in the 6th annual Boston Sharkfest, a 1-mile open-water swim in Boston Harbor. It was an absolute blast and a very unusual swim even by Sharkfest standards. The race was scheduled to start at 8:50 am with a course that went from East Boston to Southie via Boston Harbor, but it was so foggy that it was impossible to see more than a few hundred feet across the harbor, making the passage too dangerous to attempt.
seagull at the edge of Southie with a couple ships barely visible through the fog
looking out across Fort Point Channel at Boston proper
swimmers waiting in line to pick up their chips and swim caps
The race organizers decided to re-route the race down and back Fort Point Channel, which divides Southie from Boston proper. We were told to loop around "a giant pyramid" in the middle of the channel, which no one seemed to know why it was there. I later learned that the pyramid is a public art installation dating back to 2014 by artist Don Eyles.
approximate map of race course, 1.12 miles long as shown, according to http://runmap.me/
credit to Steve Bolter via https://www.facebook.com/SharkfestSwim
We were told that the water had been measured at 66 °F, although it seemed colder when I first jumped in. An older man next to me, after jumping in, kept saying "Oh, Jesus Christ. This is 66? Jesus Christ..." I had been on the fence about wearing my new wetsuit, preferring the feel and simplicity of jammers, but was very glad to be wearing it when I hit the frigid water.
The course felt distinctly urban - we swam under three bridges, with some early risers stopping to watch above, with tall buildings rising up on both sides. The channel was a good width - not too narrow for overcrowding, and not too wide that it was easy to lose your bearings. For a course that the organizers seemed to put together only minutes prior to the race, it all seemed to work out pretty well, and it was a beautiful swim. I made sure to touch the backside of Eyle's pyramid at the halfway point, noting its material, surprisingly, to be soft, probably made of something similar to polystyrene. I heard a few people afterwards saying they felt a bit grimy from the questionable water quality, but I didn't notice anything. I had expected the water to be slightly brackish due to its proximity the mouths of the Charles and the Mystic, but it tasted like regular seawater to me - quite salty.
Here are some graphs I made with the race results, with my result overlaid:
A surprising result here - non-wetsuit swimmers tended to finish faster than wetsuit swimmers, even though wetsuits are known to increase speed by increasing buoyancy and reducing drag. I suspect there is an underlying selection bias here, i.e. the sort of person to brave the cold water without a wetsuit is probably going to be in strong physical shape and tend to perform well.
This heatmap shows two semi-distinct clusters - one centered at age 20 with a 23-minute finish, and another at age 49 with a 28-minute finish. Interpolating between them, you can see that in general, people tend to slow down about 5 minutes per 25 years of age, or about 1% per year.
Overall, this was a great race and I'm looking forward to doing it again next year, hopefully across the harbor if weather allows, and perhaps a bit faster too.