An investigation by the Wall Street Journal shows a current in the Rio Olympic swimming pool may have been beneficial to swimmers on one side of the pool in the 50-metre races. Researchers have noticed this trend in the past with pools that are built especially for competition and are only erected temporarily.
In Rio, of the eight men and women who swam in the 50-metre semifinal competition, all but one of the swimmers who advanced swam in lanes four through eight. When those athletes were moved to lanes one through four during other subsequent competitions, their times slowed. Of those who medaled, five out of the six swimmers who placed in their events were swimming in the higher-numbered lanes.
Deadspin reports this exact trend was noted by University of Indiana researchers after the 2013 World Championships in Barcelona. The winners of the 50-metre races there consistently beat out their competitors on the other, lower-numbered half of the swimming pool.
In a report from swimming site SWIM SWAM, Barry Revzin, who analysed the Rio and Barcelona 50-meter data, found the swimmers in lanes four through eight had, on average, a 0.2 percent advantage against their competitors. Though it's not much, it absolutely counts when competing on a higher level like this.
Revzin called the results "very disconcerting" and wrote that while they "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."
No one can figure out exactly what causes the current except for maybe the aforementioned design of the pool. Director of the Indiana University's Counsilman Centre for the Science of Swimming Joel Stager told The Guardian swimming coaches in Rio did alert him to a current in the pool, and that they attempted to have something done but no engineering changes were made: "It's disappointing that nothing was done about it."
Revzin analysed the Rio, Barcelona, 2014 U.S. Nationals, 2015 Worlds, and 2016 Trials 400-metre, 800-metre, and 1,500-metre as well. Interestingly, he found that while the swimmers in higher-numbered lanes had an advantage pushing away from the start (which is why everyone looked into just the 50-metre originally), swimmers on the other side had the same speed advantage when coming back to it, again, again pointing to a current interfering with times.
You can read the entire report here.