THE HAGUE, Netherlands (Reuters) -- Sewage is a growing threat to oceans and seas, putting at risk marine life and habitats as the pollution problem escalates, the United Nations Environment Program (UNEP) said in a report on Wednesday.

The "State of the Marine Environment" report found that substantial progress had been achieved in reducing oily wastes and organic pollutants such as long-lived industrial chemicals in the past two decades but other problems had grown worse.

In many developing countries, between 80 and 90 percent of sewage entering coastal zones is estimated to be raw and untreated, said the report compiled by the UNEP global program of action for protection of marine environment (GPA).

The pollution -- linked to rising coastal populations, inadequate treatment infrastructure and poor waste handling facilities -- is putting at risk human health and wildlife as well as livelihoods from fisheries to tourism, it said.

"In the past we thought the ocean could be our sewage treatment plant," UNEP executive director Achim Steiner told a news conference in The Hague.

"But we cannot do that any more as even in the Arctic we see two-three times increase in concentration of mercury in seals and whales," Steiner said.

The report estimated that an additional $56 billion is needed annually to address the global sewage problem. UNEP said countries should make polluters contribute to the bill.

There is also a rising concern over the increasing damage and destruction of essential and economically important coastal ecosystems like mangrove forests -- needed for coastal defenses and fisheries, as well as coral reefs and seagrass beds.

Population pressure
Growing coastal populations and overuse of marine resources are the main source of the problem, the UNEP said. Close to 40 percent of the world's population live on the coastal fringe.

Threatened areas include the North Sea's bed, coral reefs in South East Asia, wetlands in North America, Southern and Western Africa, mangroves in many Caribbean countries, Ecuador and Colombia, and fisheries in Latin America.

The report also noted increasing levels of pollutants from sources like agricultural fertilizer, manure, sewage and fossil fuel burning, with the problem spreading from developed to developing countries as well.

This has led to doubling of the number of oxygen deficient coastal "dead zones" every decade since 1960, and degradation of seagrass beds and emergence of toxic algal blooms.

The UNEP highlighted progress made in reducing global oil and chemicals pollution. The world has cut oil discharges from industry and cities by nearly 90 percent since the mid-1980s.

But concerns of further oil pollution remain as climate change and the loss of ice is opening up the North East passage across the roof of the world to shipping and oil exploration.

The findings will be given to more than 60 member governments of the GPA initiative at a meeting in Beijing on October 16-20 to encourage a review of their planning and investment strategies to ensure they are genuinely marine-friendly, the UNEP said.

"An estimated 80 percent of marine pollution originates from the land and this could rise significantly by 2050 if, as expected, coastal populations double in just over 40 years time and action to combat pollution is not accelerated," Steiner said.