Russia's Prime Minister Vladimir Putin and other leaders from around the Baltic Sea hold a summit in Helsinki on Wednesday under growing pressure to clean up one of the world's most polluted seas.

Over-fished, surrounded by dirty industry and uncared for, the brackish sea is so toxic that pregnant women should not to eat the fish that are caught in the Baltic, according to Greenpeace.

The marine life is being decimated, researchers say. One hundred years ago there were about 100 000 grey seals in the Baltic but by the 1980s the population had fallen to 2-3000 because of hunting and pollution that made females infertile.

Putin and his counterparts from Estonia, Denmark and Norway, the presidents of Latvia and Lithuania, and Sweden's King Carl XVI Gustaf will discuss how to save the sick sea at the meeting hosted by Finland's President Tarja Halonen, Prime Minister Matti Vanhanen and the Baltic Sea Action Group (BSAG).

Environmentalists are disappointed that neither Germany nor Poland are sending a top leader to the summit, but they also insist that those who do attend must put into action already agreed plans.

"We know exactly what needs to be done," Sampsa Vilhunen, head of Worldwide Fund for Nature (WWF) Finland's marine programme, told AFP. "Let's now start implementing what's already been agreed. After that, we can evaluate whether or not that's enough."

Over 130 pledges of action

Organisers of the Helsinki summit say a range of companies, foundations and individuals have already made more than 130 promises of action to save the Baltic. Businesses have promised innovations to recycle nutrients from waste-water and technology to improve communications between vessels and local authorities to enhance safety.

Some 90 million people live around the Baltic Sea. Eutrophication ? the overconcentration of nutrients caused by sewage effluent and agricultural run-off carrying fertilisers into the sea ? over-fishing and the increasing marine traffic are the main threats to be tackled.

The shallow, semi-enclosed sea takes far longer than many other large bodies of water to flush out harmful substances and this has increased the toxic concentrations in fish, according to the Greenpeace group.

But there are also opportunities and sustainable industrial development could help protect the Baltic, said Mari Walls who heads the marine research centre at the Finnish Environment Institute (SYKE).

"The Baltic Sea has a lot to offer when it comes to developing environmentally sustainable technology," she said, citing the potential of algae, a product of eutrophication, as a base for biodiesel.

"A lack of real results"

The European Union and the nine countries with a Baltic Sea coastline ? Russia, Finland, Sweden, Denmark, Estonia, Latvia, Lithuania, Poland and Germany ? already cooperate to protect the marine environment through the Helsinki Commission (Helcom).

But critics say the body's good intentions have been slow to translate into concrete measures, and its action plan, aimed at restoring the sea to a good state by 2021, is lagging.

"There is a lack of real results. We haven't seen the action needed to meet those ambitions that have been presented within the Baltic Sea strategy," said Greenpeace ocean campaigner Jan Isakson.

Environmentalists say countries need to set aside national agendas in favour of the best interests of the Baltic Sea.

"What has been obvious over the years is that practically no country speaks with the voice of the Baltic Sea; they all speak with the voice of their own country and national interests," said WWF's Vilhunen.

Russia is currently the chair of Helcom. The next test of international commitment to the Baltic comes in May when it holds a ministerial meeting in Moscow.