Concerns have been raised over the Rio 2016 Olympic rowing and canoeing venue after a 'die-off' left tonnes of fish floating in the city's Rodrigo de Freitas Lake.

Fish die-offs are a regular occurrence in Rio’s waterways due to high levels of pollution, and the latest incident has seen 19 tonnes of Twait Shad fish clog up one of the venues for next year’s games.

Rio’s municipal environmental secretary has said strong rains and rising seas levels have caused the lake’s temperature to reduce leading to the incident and that oxygen levels in the water are normal.

However the Brazilian Environmental Defence Commisison (Alerj) have said the causes of the die-off were man-made, including contamination in the lake from domestic and industrial waste.

This follows fears over the safety of the Olympic sailing venue at Guanabara Bay, which was found to contain super-bacteria resistant to anti-biotics.

Event organisers had promised to reduce the high levels of rubbish and sewage that flows into the bay by 80% in time for the start of the sailing and windsurfing events in August 2016.