Sailing boats are seen for Aquence Rio, the International Sailing Regatta 2014, the first test for the Rio 2016 Olympic and Paralympic Games, at Marina da Gloria in Rio de Janeiro, on August 1, 2014 (AFP Photo/Yasuyoshi Chiba)

Rio de Janeiro (AFP) - Twenty-three Olympic medalists start trials on Saturday for the 2016 Rio Games in a bay littered with dead animals, television sets, sofas, shoes and not much clean water.

More than 320 competitors from 34 countries will take part in nine days of racing in a Guanabara Bay which has become "a huge toilet," according to Mario Moscatelli, a biologist who has been fighting for a cleanup since 1997.

The Australian team complained to the Olympic organising committee before the opening trials this week. Germany's sailing team proclaimed "welcome to the dump that is Rio" in an editorial on its website in March.

The trials involve men and women in 10 Olympic classes including 49er, Laser, 470, Fin, and windsurfing.

All are wary of falling into the water. And new warnings about the dangers started as soon as training started on Monday.

Mathew Belcher, Australia's London Olympic champion in the 470 class, had to tear plastic bags off his craft after his training on Tuesday.

- Dead Dog -

"We found a lot of plastic bottles and bags. Yesterday we saw a dead dog in the water," Belcher told the Folha de Sao Paulo newspaper.

"If the Olympics were tomorrow, we would really have a problem," he added.

An AFP photographer found a dead cat in the water during a tour of the bay on Thursday.

There are also television sets, sofas, shoes and other unwholesome items swept into the bay in the deluge of sewage that comes from Rio de Janeiro, which is struggling to be ready for the first Olympics in South America.

The water is "different," said Philipp Buhl, a Laser competitor for Germany.

"Yesterday in my first go on the water, I saw a wooden chair. It's not ideal," he told AFP.

The German team put up worrying pictures of Guanabara Bay on its website in March.

"The question remains how exactly the organizers of the 2016 Games will solve this problem. It isn’t just the garbage that is already in the water: With every rainfall tons and tons of new sewage are washed into the sea and without treatment plants the situation will not get any better," said the German commentary.

- Rio promises -

Cleaning up the bay was one of the promises made when Rio was awarded the Olympics in 2009.

Brazilian authorities say that 80% of the pollution in Guanabara Bay will be cleaned by the time the Games start on August 5, 2016.

The work is already behind schedule, as is much of the preparation for the Rio Olympics.

In April, International Olympic Committee vice-president John Coates said the buildup was "the worst" he has seen in 40 years of involvement in the world's biggest multi-games sporting event.

The IOC has embedded experts with Rio's organising committee to try to speed up work.

The environment department for Rio de Janeiro state insists there is no health risk to the Olympic sailors.

The local authorities have launched a 15-point programme to clean up the bay, according to the department website. The first is to work with the 15 municipalities around the bay to stop untreated sewage gushing in.

The environment department would not say how far the programme has advanced.

One attempt to clean up Rio bay after the city held a world environment summit was closed again in 2006 with little apparent progress.

The Inter-American Development Bank and the Japan International Cooperation Agency put one billion dollars into the cleanup. But the funds appear to have evaporated into thin air. The pollution has not.