Floating trash in Rio de Janeiro’s picturesque but polluted Guanabara Bay has forced organisers to switch venues for an Olympic sailing test event.

The men’s and women’s events in the 470 two-person dinghy last Friday had to be moved from the Bridge course because of “objects in the water”, the International Sailing Federation (ISAF) said in a statement.

The events were initially moved to another course, Niteroi, but a lack of wind there forced organisers to move them yet again, to the Naval School course, the ISAF said.

In all, there are six sailing courses planned for the 2016 Olympics in Brazil, the first to be held in South America. Three courses are inside the bay and three on the Atlantic Ocean.

But the postcard-perfect backdrop of the bay has been overshadowed by pollution concerns.

Huge amounts of raw sewage from the Rio urban area currently pour into the bay, along with floating garbage, discarded furniture, dead animals and other debris.

With less than a year to go until the Games open on August 5, city officials have acknowledged they will not be able to keep their initial promise to clean up 80 per cent of the pollution.

That has raised health fears for athletes and concerns that floating trash could disrupt events.

That happened during another test event on Saturday, when two Brazilian sailors’ Nacra 17 boat tipped over after their rudder snagged on a garbage bag.

Authorities have dispatched 20 trash boats to scoop up the debris and installed “eco barriers” around the courses to try to hold the trash back.

The ISAF said it is working closely with Rio officials to address the issue of water quality.