In a new report, released in the Brazilian city of Rio de Janeiro, the WWF says that more than half of all freshwater species are in decline and that marine life is also being seriously damaged.

According to the report, if these trends are to be reversed, drastic action will need to be taken, including a making a massive cut in the level of carbon dioxide emissions.

This is the second edition of the WWF's so-called Living Planet Report. It is an assessment of the state of global bio-diversity and the impact which human activities are having on the planet.

Worrying findings

"Everything we do to the natural environment has an effect on plants and animals," says Jonathan Loh, the author of the report.

The report measures the decline in the world's forest cover and the rate at which marine and freshwater animals are disappearing. Its findings are not encouraging.

The Guanahacabibes Robber Frog from Cuba (WWF-Canon/Kevin Schafer)

According to the WWF, freshwater amphibians are particularly under threat. Frogs, toads and salamanders are particularly sensitive indicators of an ecosystem going awry because they breathe through their skin.

In Australia and the United States, several species of frogs have become extinct and it is not always clear why. However, the report says fertilizers and pesticides are being used on a scale never seen before, with devastating consequences for the world's rivers.

Of the 281 freshwater species studied as indicators of water quality, the numbers of just over half were on the wane.

Negative trends

About 60% of the world's fishing waters are being exploited to the limit or over-fished, says the WWF. It also calls for action to prevent soil from becoming eroded by overgrazing and says Europeans and North Americans should cut their consumption of meat and dairy products.

Deformities are worrying scientists

"This report is a graphic call to reduce these negative trends as the world enters the 21st century," WWF Director-General Claude Martin says.

"The observed declines in populations of freshwater species is particularly alarming as they indicate the extent of deterioration in the quality of the world's rivers, lakes and other wetlands."