Brazilian environmentalist and biologist Mario Moscatelli says sewage has killed at least a ton of fish in a lagoon next to the Olympic Park that will host many Rio 2016 events.

Moscatelli said Saturday that thousands of tilapia, sea bass and mullets started washing up Friday on the shore of Rio de Janeiro's Jacarepagua Lagoon. He said the die-off could be repeated during next year's games.

"The lagoon is not one of the Olympic water venues but it does embrace the Olympic Park," Moscatelli said.

He said the fish most likely died because of insufficient oxygen due to pollutants and untreated human waste flowing into the lagoon from nearby condominiums and sprawling shantytowns.