[2] The location for open-water events was a source of concern for athletes since scientists have found microbes in the waters off of Fort Copacabana and drug-resistant super bacteria off the beaches of Rio de Janeiro in 2014 and 2016 studies due to the daily dumping of hospital waste and household raw sewage into the rivers and ocean.

Ten percent of the Copacabana water test samples contained drug-resistant super bacteria.

[5][6] Similar to the program's format in 2012, swimming features a total of 34 events (17 each for men and women), including two 10 km open-water marathons.

For the pool events, prelims are held in the afternoon, followed by the semifinals and final in the evening and the night session (due to the substantial fees NBC has paid for rights to the Olympics, the IOC has allowed NBC to have influence on event scheduling to maximize U.S. television ratings when possible; NBC agreed to a $7.75 billion contract extension on May 7, 2014, to air the Olympics through the 2032 games[7] and is also one of the major sources of revenue for the IOC).

[13] Each relay event features 16 teams, composed of: The men's and women's 10 km races at the 2016 Summer Olympics featured 25 swimmers:[14] Brazil, as the host country, receives guaranteed quota place in case it would not qualify any qualification places.