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Race Tips

Data Dive: The Fastest Ironman and 70.3 Swim Courses

Looking for a little (legal) assist in the swim leg of your next race? Data scientist Alfredo Molinas breaks down the stats to find the fastest Ironman and 70.3 swim courses.

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It’s no secret that many triathletes prefer the bike or run over the swim, and will gladly welcome any opportunity to be done with the water as quickly as possible. And those triathletes who raced in Oregon 70.3 earlier this month looking for a quick swim were in for a nice surprise: the downstream course down the Willamette River allowed athletes to clock incredibly fast swim times. The average for age-group finishers was only 24:04! Once again, that’s a 1.2-mile swim in 24 minutes. If we compare to Kona-qualifying 70.3 races over the last five years, that is 13 minutes faster than the average.

If you are looking to fly through a swim course PR but missed your chance at Oregon, where else should you consider?

The Fastest Ironman Swim Courses

Looking back at the last five years of competition (and removing those races which had shortened/canceled swim legs), we expect to see Chattanooga and Cozumel, world famous for their fast swims, at the top. We also see Italy, North Carolina, and Brazil in the top 5. These swims are almost 25 minutes faster than the bottom 5. That time difference alone won’t make a huge dent on your total race time, but you’ll probably be glad to have that extra energy for the bike and the run. And if swimming is not your favorite, it might feel like a long start to the day at Mont-Tremblant, Maastricht, Switzerland, Taiwan, and Florida.

The chart below shows the full range of the swims from Kona qualifying races since 2016. The legs are color-coded to show what kind of swim they were: red is for river swims, yellow is for lakes/reservoirs, and blue is for oceans/bays. In full Ironman races there aren’t many river swims (they are much more common in 70.3 races), and they generally tend to lead to faster swims, as with Chattanooga or Australia. We can also see that while ocean swims can be relatively fast, lake swims, on the other hand, tend to be connected with slower swims. This is likely explained by less friendly currents and decreased buoyancy from swimming in freshwater.

On the topic of buoyancy, one might expect wetsuit-legal swims to have faster results than races where wetsuits are not allowed—i.e. in warmer waters. However, we find no strong correlation there, as the few races where wetsuits are not allowed seem to be spread out fairly uniformly across the ranking. There are bigger factors affecting whether or not you’ll have a fast swim, so don’t let the lack of wetsuit hold you back!

RELATED: Do Wetsuits Really Make You Faster? The Science Says…

Instead, the real secret to a fast swim lies behind the course design. Most swims are loops with one or multiple laps, starting and finishing in more or less the same spot. This means that whatever benefit you get from a friendly current will at some point work against you as you complete the loop. However, swims which are point-to-point, that is, those which start in one place and finish in a different place, can take advantage of the current to push swimmers along in one direction. This is what we see in Chattanooga (river swim), Cozumel (ocean swim), and Brazil (ocean swim), and why we are unlikely to see something like that in a lake swim.

Average Ironman Swim Finish Times

A chart of the average swim splits at Ironman Swim Courses

RELATED: Data Dive: 9 Takeaways on Qualifying for Kona

The Fastest 70.3 Swim Courses

We can take those learnings and apply them to the world of 70.3 as well. Although the data is a bit spottier, the subset of 70.3 races that were Kona qualifiers in the last few years (Ironman offers Kona slots at a handful of 70.3 races each year) give us a good picture of where the fastest 70.3 swims lie. I added Oregon to the chart below, to show just how much faster it was than these already-fast swims. We see once again that river swims are generally faster and lake swims generally slower. In the end, though, having a point-to-point course design will probably be a determining factor. This is what we saw in Oregon: a river swim that takes full advantage of the current by finishing downstream from where it began. 

Fastest Ironman 70.3 swim times (Kona-qualifying 70.3s)

A chart of the fastest 70.3 swim courses

The bottom line on fast Ironman swim courses

Chattanooga and Cozumel are old classics for those looking to feel like they are swimming downhill, but there are many other courses out there with fast swim legs. Keep a lookout for swims that are either on rivers or oceans and have a different finishing place than the starting point—although if you enjoy being in the water, a lake swim at Mont-Tremblant might be the thing for you.

RELATED: How to (Finally) Become a Faster Swimmer