SÃO PAULO, Brazil — Heavy rains in Rio de Janeiro caused an ecological nightmare at the lagoon where Olympic rowing will take place in 2016, when 65 tons of dead fish were discovered earlier this week.

According to USA Today, the rain depleted the lagoon's oxygen levels when rotting plant matter was washed into it, killing the yellowtail, catfish, tilapia and sea bass that live in the waters.

More from GlobalPost: Are you ready, Rio? Brazil braces for Olympic 2016 spotlight

Environmental authorities launched a cleanup of the Rodrigo de Freitas Lagoon, reported The Guardian.

City workers had to move quickly, as rowing qualifiers for the 2016 Olympics started Thursday, according to New Scientist.

The Associated Press reported that no dead fish were pulled out of the tourist attraction as of the day of the qualifiers.

A similar incident in 2009 left 100 tons of fish dead and needing to be removed from Rio's central lagoon.