Trawling for trash in Rio Games clean-up

A stout green catamaran plies the polluted waters of Rio de Janeiro's Guanabara Bay alongside the fishing boats, but instead of grouper and swordfish its catch consists of plastic bags, soda bottles and even a discarded toilet seat.

The catamaran is one of three so-called "eco-boats", floating garbage vessels that are a key part of authorities' pledge to clean up Guanabara Bay before it and other Rio waterways host events during the 2016 Olympics. Critics say the boats do little to address the more pressing issue of sewage.

With limited garbage and sewage services in this sprawling metropolis of 6 million people, tonnes of garbage and raw waste flow daily from sludge-filled rivers into the bay, where Olympic and Paralympic sailing events will be held. At low tide, mountains of household refuse, old sofas and even washing machines are seen.

An Associated Press analysis in November of more than a decade's worth of Rio state government tests on waterways across the city showed faecal coliform pollution levels far above those considered safe by Brazilian or US law.

That pollution means nearly all beaches dotting the 383 square kilometre bay have long been abandoned by swimmers, and some health experts warn of risks to athletes who come into contact with the water. Sailors warn that high-speed collisions with floating detritus could damage or even sink yachts.

Water pollution issues began making headlines in Brazil's local press again in recent days, after thick patches of brown foam appeared along the city's most popular beaches such as Copacabana as the southern hemisphere summer hits full stride. Rio's beaches, overwhelmed with holiday visitors, have been inundated with trash, much of it floating in water just metres from the sand.