Was There a Problem with the Rio Pool?

Barry Revzin has seemed to notice something very interesting about the pool in Rio. He has shared with us the information below on his thoughts including data and explanations.

I have been obsessively watching every session during the Olympics with friends (really all of us watching on our own, thousands of miles apart, but filling a WhatsApp group chat with several hundred messages a day), and during one of the sessions there was a throwaway comment by either one of the commentators or one of the swimmers about how somebody was swimming faster in one direction than another. That seemed overly suspicious to me, so I decided to check it out.

Could there be a current in the pool? (Again?)

To start with, I took a look at all the splits of the finalists in the men’s 1500m and women’s 800m freestyles and compared how they swam their races in prelims to finals to see if lane assignment had any effect. You would expect swimmers at this level to have a clear race strategy, particularly those right on the cusp of making finals. And you would expect distance swimmers to roughly even pace the middle parts of their races. But that’s not really what happened. Instead, we have a lot of jagged splits – swimmers consistently going faster in one direction than another. Furthermore, Belmonte Garcia and Leah Smith, when they switched which side of the pool they were on, actually inverted in which direction they were swimming faster:

w800-Barry Revizn

You can see the same in the mile, with Horton, Cochrane, and especially Christiansen (who had the largest lane shift – six lanes to the right):

m1500 barry Revzin

At this point, this is just an interesting anomaly (along with the general “jaggedness” of the splitting as a whole). There could be something there that’s pushing the swimmers towards the turn end in lanes 1-4 and towards the start end in lanes 5-8.

So let’s think bigger. I took a look at all the 400s, 800s, and 1500s swum in the last five major meets for which I could find both splits and lane assignments: Barcelona 2013, US Nationals 2014, Kazan 2015, US Olympic Trials 2016, and Rio 2016. I skipped swimmers for whom there were incomplete splits as well as one who was time trialing a shorter distance during the longer one(see note 1). I also dropped the opening and closing 100m from each race. For the rest, I took a look at the lap over lap percentage change in split time and adjusted it for direction (see note 2). I would expect these distributions to be roughly around 0 (with some noise) and completely independent of lane. Certainly you don’t split your race from lane 1 any differently from lane 8 right?


My expectations are definitely met by the results from Nationals in 2014, Kazan in 2015, and from Trials in 2016. Each lane’s distribution is right around zero, there’s not any clear differentiation from one lane to another. But Barcelona and Rio were dramatically different. In both pools, there was a clear drift from lane 1 to lane 8 – which suggests that swimmers were pushed towards the start end in the upper lanes and pushed towards the turn end in the lower lanes, with the effect greater the further you get from the center. This is very concerning.

Edit: this previously said that the effects would even out – which they would not.

Even with a circular current, there would be effects that don’t even out over the course of a long race. These add up to a few tenths of a second for the swimmers in the outer lanes of the 800 and the 1500. In a race that was decided by seconds, this would not have affected the final result ordering. But in a 50, a difference of a couple tenths of a second due to a push or a pull could be the difference between a medal and not. It’s hard to know how fast a swimmer should go in a 50, but thankfully we can compare multiple performances by the same swimmer from heats to semifinals to finals. If a swimmer moves from a purportedly unfavored lane (like 2) to a purportedly favored lane (like 7), does that lead to a faster time? We would definitely expect it not to! I looked at all the 50s (all strokes where possible) across the same five meets (no stroke 50s in the Olympics so fewer data points in the Trials and Olympics charts) and tried to tease out the impact of lane change (simply new line minus old lane) on performance improvement (new time divided by old time). For instance, Etiene Medeiros swam a 24.82 in prelims out of lane 2, then a new South American record of 24.45 in the semifinal out of lane 8, then a 24.69 in finals out of lane 1. This means that with a lane change of +6, she had a performance change of -1.49%, and with a lane change of -7 she had a performance change of +0.98%.

Here are the full results, along with lines of best fit and regression statistics:


As before, we see basically no impact in Nationals, Kazan, or Trials. Very low correlation, and the slope has very little predictive power. Perfect.
But in Barcelona and Rio? That’s a tremendous effect. 48% of the improvement in time in Rio, and 36% in Barcelona, can be explained by moving from the left hand side of the pool to the right hand side, with an extremely small pvalue. The slope is large as well, 0.2% improvement per lane as swimmers move to the higher lane numbers. That doesn’t seem like a lot, but consider that 2nd through 4th place in the womens 50 free came from the favored lanes and just 0.1 seconds separated Simone Manuel in 2nd (from lane 7) from Ranomi Kromowidjojo in 6th (from lane 3). That’s 0.4% of the race, and it looks as if Manuel got a relative 0.8% boost.

These results are very disconcerting to me, but do not in and of themselves prove that there is a problem. However, the data strongly point to serious problem in the pool which could have led to an unfair competitive environment, especially in the 50m freestyles. I think it should be investigated.

1) Marcelo Acosta in Kazan split his 800m at 3:52.8 / 4:19.6. It was an extreme outlier in the dataset as far as split consistency went, so I think it’s safe to exclude.
2) For example, here are the first few splits of Henrik Christiansen’s finals performance in Rio after dropping the first 100 meters. It’s the last row that I’m interested in, which ensures that the alleged current has the same sign in both directions:

150 200 250 300 350 400
Split 30.09 29.75 30.1 29.7 30.11 29.72
% Diff -1.13 1.18 -1.33 1.38 -1.30
Adjusted % -1.13 -1.18 -1.33 -1.38 -1.30

To find out more about this, go to Barry’s next other post. This was written by and courtesy of Barry Revzin.

Leave a Reply

Notify of
newest most voted
Inline Feedbacks
View all comments
5 years ago

None of the .png files in this article are showing!

Reply to  Sprintdude9000
5 years ago

They are for me…

Reply to  IMer FTW
5 years ago

The problem was fixed within an hour of my comment, so please ignore it!

5 years ago

Bucknell and UVA also have drafts/currents when they are in their 50 meter set up. Depending on the flow of water, overflow, etc, this can happen. It sucks, and is really evident when observing multiple heats.

Thanks for posting this!

Reply to  SwimmerCoach
5 years ago

Bucknell University is notoriously bad when it is set up for LC meets- unless a swimmer is lanes 4 or 5, they face a current. Swimmers hope for good lane placements in every heat, otherwise they swim the current.

5 years ago

Very interesting. As sprintdude said, can’t see the data right now so I have to take your assessment at face value, but I am intrigued. Can’t remember what lanes everyone is in but it might have contributed to Chalmers’ unreal back half, Cate’s overly aggressive race/rough finish, or any number of other surprises.

Steve Nolan
5 years ago

Should’ve mentioned it last week, would’ve put a little sailboat in the pool and noted where it went.

5 years ago

They can still test and fix it for the paralympics next month. And I would guess its already been tested before the meet. Didnt this already happen somewhere? I think it was Barcelona or one the world championship meets. I think the solution was to temporarily shut the pumps off while the competition is going.

Reply to  Taa
5 years ago

I hope they do! Or at least, I hope somebody performs some physical tests to verify the existence of such a current.

5 years ago

Look at the results of the Women’s 50 free. The finalists were separated by just a few hundredths.

Lane 7 and 8 got the silver and bronze.

How would you feel if you lost an Olympic medal because of the pool?

Caeleb Dressel\'s Occupied Stall
Reply to  Marklewis
5 years ago

Now that you mention it i seem to remember one end of the pool clearly ahead of the other in general in the womens 50 free, although ill have to rewatch the race to make. I wonder if pool currents had something to do with that

Reply to  Caeleb Dressel\'s Occupied Stall
5 years ago

There were more than a few crazy performances in the women’s 50m free; Garcia’s Puerto Rican record of 24.94 from lane 8 in the heats and Medeiros’ South American record in the semis (also lane 8) come to mind

Reply to  Marklewis
5 years ago

@Marklewis while I agree that the pool was probably a train wreck like the rest of the Rio games (i.e. Diving, robberies, etc.) you have to remember that almost all 50’s in general at any national or international swim meet are separated by very small fractions of seconds. While the pool probably had currents, most 50’s are like this, winner or loser by a .01 of a second

5 years ago

Finally an excuse is found for some of our swimmers’ poor performances.

Reply to  Prickle
5 years ago

You mean NOT EVERY US SWIMMER MEDALED AND BROKE WRS?!?!?! dang they must suck soooo bad, not like they were up against the best in the world, not like conditions may have been sub par. Not like some of them may not have had the meet of their life on that particular day,hour, or minute of their swim.

Reply to  Swims
5 years ago

@swims Yes, I 100% agree, I don’t want to say that swimming is luck because it’s not, but swimmers train in sub par pools, swimmers ALL have bad races some days. You couldn’t be more right.

Farty McFart
Reply to  Prickle
5 years ago

You mean Missy Franklin?

Oliver Kramer
5 years ago

This german Website found out exactly the same: http://swim.de/aktuell/zwischenzeitenanalyse-von-swimde-belegt-stroemungen-im-olympiapool-66698

So swimmers were betrayed!