Rio de Janeiro's waste management company is cleaning up dead fish after a die-off at a lake that's slated to hold Olympic rowing competitions during the 2016 games.

Dead fish have been washing up on the banks of the Rodrigo de Freitas lake for several days.

Fish die-offs are a frequent occurrence in Rio's waterways, which are filled with raw sewage and garbage.

The city's environmental secretariat said the latest incident is the result of recent rains and high sea levels, which caused the lake's water temperature to plummet.

Rio's water quality has become a contentious topic ahead of the Olympics, which will see sailing, rowing and other events.

Authorities had pledged to clean up the water ahead of the games, but now admit those promises won't be met.