File picture shows a partial vew of the Cunha canal that flows into the highly polluted Guanabara Bay in Rio de Janeiro, Brazil, venue for the 2016 Olympic sailing competitions (AFP Photo/Christophe Simon)

Rio de Janeiro (AFP) - Dozens of demonstrators gathered at Rio de Janeiro's heavily polluted Guanabara Bay, demanding that officials clean it up before it is used as a 2016 Olympic sailing venue.

Amid whistles of disapproval and shouts of "shame!" demonstrators held a beachside protest, their boats symbolically kept on the shore as they waved their oars in the air.

They launched their protest at noon to coincide with low tide, when the dirtiness of the water is most evident.

"Brazilian authorities promised a series of improvements to the bay but just a little more than a year ahead of the Olympic Games have done virtually nothing," said Mario Moscatelli, a university professor and biologist, who called the protest.

Athletes training for next summer's Olympic Games have complained about the condition of the water, where animal carcasses, sewage and tons of dead fish have been found floating.

From the shore, the demonstrators displayed examples of the trash extracted from the bay, including an intact toilet.

Moscatelli called the continued high levels of pollution the result of a "lack of leadership."

At the time of Rio's candidacy to win the Games, city officials promised to clean up 80 percent of the bay's waters, but so far they have managed only to clean about 50 percent.

Next year's Games are set to take place August 5-21.