By Alex Kirby BBC News Online environment correspondent

A report prepared for the United Nations says sewage levels classed as acceptable are making people ill.

It says standards in the US and Europe are failing to protect swimmers properly.

The report says shellfish affected by sewage are killing tens of thousands of people every year.

It wants priority given to lowering sewage levels, which it says are also causing significant economic losses.

The report, Protecting the Oceans from Land-based Activities, was prepared by a UN-sponsored group of experts on the scientific aspects of marine environmental protection.

It is being presented to a meeting of the Global Programme of Action for the protection of the marine environment from land-based activities (GPA), which starts in the Canadian city of Montreal on 26 November.

Handy sewer

The director of the UN Environment Programme (Unep), Dr Klaus Toepfer, said: "The oceans cover 71% of our planet's surface, regulate its climate, and provide its ultimate waste disposal system.

"And yet our species continues to treat them as our common sewer."

Unep estimates the value of marine and coastal ecosystems at about �8.5 trillion ($11.9 trillion), roughly half the annual global gross national product.

Sewage can blight coastal waters

Dr Toepfer said about 80% of the environmental problems of the oceans started on land.

"It is here that most of the pollution originates", he said, "whether from factories and sewage works at the coast, from fertiliser or pesticides washed into rivers and down to the sea, or from chemicals emitted from car exhausts and industry and carried by the winds far out to the oceans."

The GPA report says the damage land-based activities are causing to coasts and seas is increasing both in kind and degree.

It says the top priorities for action are:

• the physical alteration and destruction of habitats
• excessive inputs of nutrients, causing rapid phytoplankton and algal blooms to grow, starving sea life of oxygen
• changes in sediment flows
• the impact of sewage on health.

Even brief exposure can be risky

A World Health Organisation report estimated that one bather in 20 in waters defined as acceptable would become ill after going into the sea just once.

The GPA report says that eating sewage-contaminated shellfish raw causes about 2.5 million cases of infectious hepatitis annually, killing 25,000 people and causing as many long-term disabilities through liver damage.

Irrelevant standards

Other diseases linked to sewage in seawater are cholera and typhoid.

Vicky Garner of Surfers Against Sewage told BBC News Online: "The EU standards were set in 1976, and they're widely accepted now as having little relevance.

"We know we can swim off an officially approved beach and get ear, nose and throat problems, gastro-enteritis or even hepatitis A.

"There are tentative suggestions of a link between sewage and viral encephalitis, and also meningitis."