A flotilla of more than 30 boats and water craft has cruised across Rio de Janeiro's Guanabara Bay to protest against water pollution with a year to go before the 2016 Olympics.

The protesters made the 12 kilometre journey to highlight high levels of bacteria in the bay.

Trials for the events are due to start in Rio waters next Saturday with the authorities in Rio initially hoping that 80 per-cent of the bay would be cleaned up in time for the Games, but they have admitted more recently that they would not meet these targets.

Protesters are concerned about the health of the athletes taking part in Olympic sailing competitions.