Data Dive: The Fastest Ironman and 70.3 Swim Courses (2024 Update)

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. It’s also no secret that the swim is one of the hardest disciplines to see major improvement. That’s why, as a service to those looking for a swim PR, we’ve broken down the available data from last year’s swims at Ironman and 70.3 races – nearly 150 in total – to see if we can find any patterns. If you want to find the fastest Ironman and 70.3 swim courses around the world, read on!

The different types of Ironman and 70.3 swims

Across the 35 Ironman races that had a full swim (that is, not shortened due to weather or unsafe conditions), nearly half took place on some sort of lake or reservoir. Just over a third took place in the open ocean (34%), and river swims were only 11% of all the swims.

On the 70.3 circuit, we saw a different makeup of swim courses. Ocean swims were actually the most common (38%), which together with bay swims make up half of all 111 races looked at in the last year. Lake swims were 31% of the distribution, reservoir 6%, and we saw one fjord swim in Sandnes, Norway. In short, full Ironman distance races feature slightly more lake swims, while in 70.3 races there are relatively more ocean swims.

Average Ironman swim times, by course

In discussing the fastest and slowest Ironman swim courses, we must begin with a special mention to both Chattanooga (0:48) and California (0:50) – both river swims with currents so friendly, they were more than 20 minutes faster than the swim in Brazil (1:10), which is historically famous for being very fast.

We can see from the picture below that none of the lake swims analyzed in this dataset were very fast, but neither were they very slow. Those went to Kazakhstan (1:30), Korea (1:32), and Subic Bay (1:42), which averages almost a full hour slower than Chattanooga.

Average 70.3 swim times, by course

Over in the half-distance realm, a special mention to 70.3 Maine (0:20), a full 4 minutes faster than Oregon (0:24) – which was the previous year’s fastest swim course – and over 10 minutes faster than the third-fastest 70.3 swim course in Ireland (0:30).

As with the Ironman races, 70.3 lake swims were neither too fast nor too slow on average. In fact, they have the smallest variability of all the other types of races. Again this makes sense – sometimes river/ocean currents can work in your favor, and other times, depending on course design, they can make things much harder.

Last year, 7 out of the slowest 10 swims were in Asia. While many of those races can be challenging due to climate conditions (running in the middle of the day in the tropics is no easy feat), it is also quite possible that the difference in times relative to the rest of the world also reflects the relatively nascent stage of the sport in the region in general.

A note on water temperature (and wetsuits)

This year we had a lot more reliable data on water temperature at each race, so we are also able to see if temperature has any impact on swim time. This is important because it indirectly says something about the usefulness of wetsuits for giving us an extra boost.

Looking at the 111 70.3 races of 2023, we can see that there is indeed a positive trend between the temperature and time. That is, the warmer the water, the slower the average swim time tends to be. Note that the points are quite scattered, which suggests that the impact of water temperature on your swim time is not that great. Bringing this to the perennial wetsuit debate, wearing one will probably give you some boost, but there are other factors with stronger impacts on your swim. Note that we also don’t see a huge jump at the 24°C point, which is the cutoff temperature for wetsuits! (For more on this, check out How Much Faster Does a Wetsuit Make You?)

As you prepare your racing calendar for 2024, if you’re looking to finish the swim early, head for the speedy rivers in North America, or look for ocean swims like Brazil that start and end in different places and can take advantage of the current. Just remember that sometimes currents can also work against you, so if you’re looking to hedge your bets, the more peaceful waters of lakes and reservoirs will really force all your hard swim training to come out.

Still deciding on which race to do in 2024? Perhaps these data dives will help:

• The Fastest and Slowest Ironman Races of 2023
• The Fastest and Slowest 70.3 Races of 2023