HWACHEON, South Korea — The conflict between North and South Korea has claimed hundreds of thousands of human casualties over more than half a century, but the latest group at risk is a different species entirely — the otter.

At first South Korean engineers feared the waters would cascade from North Korea, flooding towns and farms, rising above the banks of the mighty Han River as it bisects the capital of Seoul, 80 miles to the southwest.

By now, however, the waters have receded to a trickle as the north branch of the Han flows sadly across the demilitarized zone between the two Koreas. The worry is that species of plants and animals will die and life will never be quite the same in forested hills and valleys rising from the river. “In the past this region was under water,” says Kang To Il, pointing from the roadway atop the Peace Dam, completed two years ago as fears rose that the Kumkang Dam, 15 miles to the north, above the Demilitarized Zone between the two Koreas, would collapse, unleashing billions of gallons that energy-starved North Korea now pumps through a hydroelectric power station and then out to sea.

“Trees and grass down there started to grow after the Kumkang Dam was built in 1999,” says Mr. Kang, an official of Hwacheon County, whose 25,000 residents make it one of South Korea’s least populated districts. “Fish cannot come down,” he goes on, and animals such as otters that rely on the fish for food are hardly seen, though footprints and droppings indicate their presence.

As Mr. Kang talks, he points to South Korean guard posts glimmering on a ridgeline six miles to the north. South Korean soldiers are up there defending the southern side of the Demilitarized Zone that stretches 155 miles across the Korean peninsula, dividing North from South Korea.

Another seven miles beyond the zone, in mountains stripped for firewood by impoverished North Koreans, lingers the dam whose construction began more than 20 years ago in a desperate attempt to revive the North’s swiftly declining economy.

It was in response to the North Korean project, scrutinized by American spy satellites, that alarmed South Korean leaders in 1986 ordered construction of the Peace Dam. The dams are nearly the same size — the Kumkang Dam, named for the Kumkang or Diamond mountains surrounding it, is 121.5 meters, the Peace Dam 125 meters high.

“The dam was built higher to contain the water in case of collapse,” explains Mr. Kang, but the river, with banks overgrown by grass and shrubbery once entirely covered by water, meanders far below.

It is a harsh fact of the North-South confrontation that no one from the South Korean side has ever been able to communicate with anyone from the North about the Kumkang dam and the dangers it poses of flooding in case of a break, as happened a few years ago in the midst of construction, or of robbery of much needed water.

Han Sung Yong, director of the Korea Otter Research Center, dedicated to saving the 100 or so otters that are believed to survive here, passed along a message in early October when South Korea’s president, Roh Moo Hyun, met North Korea’s leader, Kim Jong Il, in Pyongyang.

While the leaders were holding their summit, a professor in Mr. Roh’s entourage raised the topic of the Kumkang Dam with some North Koreans to see if the two sides could cooperate on conservation. So far, there’s been no response.

“North Korea is a closed society,” says Mr. Han. “North Korea doesn’t want to discuss this issue.”

A senior research fellow at the South Korean government’s Korean Institute of National Unification, Son Gi Woong, sees the impasse in terms of North Korean desperation.

“For their national interests, they have no choice but to stop the water,” he says, even as deforestation has exposed large swaths of the North Korean countryside to floods while stripping it of topsoil for crops.

“Because of lack of energy,” Mr. Han goes on, “they have to cut the trees down,” just as they had to build the Kumkang Dam.

In a park below the Peace Dam, authorities hope to get across a different message. Craftsmen are casting an enormous “peace bell” that will ring so loudly that North Korean soldiers will be able to hear it.

“The bell will ring out new life through shadowy valleys of war, death and destruction,” says a government brochure.

“I’m not interested in politics, just in facts,” says Mr. Han. “The situation will get worse and worse.” He worries especially about the otters, bellwethers of deeper problems.

“The gap in the water level in non-dry and dry seasons is very big,” he says. “The otters have been most affected. They cannot endure such differences.”