The tidal flats along Okgu on South Korea's southwest coast are drying out and endangered birds have fled toward the Yellow Sea in search of food.

The fishermen who depend on the 40,000-hectare Saemangeum wetlands for shellfish complain their catches have plummeted by 75 percent and say they cannot take their boats out.

The reason is a 33-kilometer sea wall that was completed in April, over the objections of environmentalists who fear it will destroy one of Asia's most important wetlands - akin to Chesapeake Bay in the United States or the Wash in England.

The government is spending four trillion won (HK$32.8 billion) on the world's longest sea wall as part of a development drive that has converted about half the country's 400,000 hectares of tidal flats to farming and industry since 1960.

Destroying coastal wetlands is nothing new in Asia. Japan, Singapore, Macau and Hong Kong have all done it.

Singapore has reclaimed 104 square kilometers since 1965, while China reportedly has taken half its coastal mangrove forests since 1949 for land reclamation and aquaculture.

Japan sparked an international outcry in the 1990s when it began building a 7km dike around its largest tidal wetlands on Isahaya Bay. A court last year allowed the project to continue, despite environmentalists' concerns it is destroying bird habitat.

"In many parts of Asia, particularly developing countries, coastal wetland are under great threat because they are being used for port facilities, urban development and agriculture development," said Taej Mundkur of the Asia Pacific Migratory Waterbird Conservation Strategy.

South Korea's government says it conceived the Saemangeum project during a food crisis in the 1970s and argues it will alleviate flooding, provide a new source of clean drinking water and create much-needed farm fields in a country where 65 percent of the land is mountains.

Successive governments have supported the project, started in 1991, and is backed by politically powerful agriculture interests. Farmers say the project also will help reduce annual flooding that can inundate some 12,000 hectares of crops in the basin of the Dongkin and Mangyung rivers.

Fishermen say that while the project may boost farm employment, they fear it threatens 25,000 jobs tied to the sea.

Environmentalists argue it will decimate migratory shore birds.

Hundreds of thousands of birds, including endangered Nordmann's greenshanks, spoon-billed sandpipers and black-faced spoonbills, stop at the wetlands from March to late May. It is one of the few feeding sites for shore birds along a migratory route running from New Zealand all the way up to Alaska.

A loose knit coalition of Buddhist monks, fishermen and bird watchers banded together trying to halt the plan, marching 290km to the capital, blockading the construction site with boats and filing lawsuits that caused temporary halts. But South Korea's Supreme Court ruled in March there was insufficient evidence the project would harm the environment and allowed it to proceed.

Due to be finished in 2011, the project will create an 11,800-hectare freshwater lake and turn the rest of the marshy expanse into farmland and possibly a golf course.

"The developers say trust us. Don't worry, it will be OK," said Nial Moores, 43, a Briton who heads Birds Korea. "They say the birds will move somewhere else, the tidal flats will re- form. This is a fallacy. There is no evidence from anywhere else in the world that tidal flats can re-form in deep sea water. There is no evidence from anywhere else in the world that shore birds can simply move somewhere else."

Saemangeum - a muddy and sandy stretch of coastline alternately exposed and covered by tides from the Yellow Sea - is one of the few feeding sites for shore birds along the New Zealand to Alaska migratory route.

There are only 10 such ecosystems in the world. And researchers say the wall's impact will likely repeat that of others where bird numbers fell dramatically.

Already, dead shellfish litter the flats while bird numbers have dropped 30 percent in the past five years.

The sea wall also could hurt conservation efforts as far away as Australia and Alaska.

"No matter how well we do it in Australia and New Zealand, it is all for nothing if the middle link in the chain is not getting the same kind of attention," said Australian researcher Danny Rogers.

The government insists the project will be "environmentally friendly" and predicts shore birds will move to other tidal flats along the Yellow Sea. But it acknowledges the project could lead to a drop in shore birds using the area.

"Even though the tidal flats will disappear, the birds won't just die," said Kang Chang Hyun of the Korea Rural Community and Agriculture Corporation. "Besides, we are building a freshwater lake that will attract other species."

For the fishermen in villages like Okgu, the concerns are more practical.

Gathering in a community center under a sign reading "Protect People's Right To Survive," fishermen recounted how the falling catches in Saemangeum have left many strapped for cash and led to increasing drunkenness and domestic violence.

Though the government has offered villagers thousands of dollars in compensation, many appear overwhelmed by the prospect of having to abandon a way of life that has supported the village of 1,200 people for decades.

For humans, the court fight is over. For the birds, the kilometers of mud flats soon will be gone.

ASSOCIATED PRESS