HILLSBOROUGH - They set out to stop a dam and created the state's first land conservation trust, protecting 5,000 acres in Durham and Orange counties.

The Eno River Association is marking its 40th anniversary and honoring those early members who laid the foundation for protecting the water and its banks.

"We're kind of celebrating all year," executive director Robin Jacobs said while hunting down addresses of members and volunteers for a private party in February.

The people who were there at the start agree that the association came about thanks to the energy and tenacity of Margaret Nygard, who died in 1995.

She and her husband, Holger Nygard, learned of Durham's plans to build a reservoir on the Eno when they first moved into their Cole Mill Road home.

"When we started, it was not like saying, 'Today shall be born the river association,' " said Holger Nygard, a retired Duke University English professor. "When we heard that this beautiful property was threatened by a dam, we became incensed."

Soon they and neighbors were organizing nature hikes and canoe trips to raise awareness about the river.

Duncan Heron, a retired Duke geology professor, remembers the day he and a friend pulled a canoe from the water near the Nygards' home. Margaret heard the commotion, came down to the riverbank and invited them up to the house for a drink.

"She had a genius about her for getting people interested and involved in the river," Heron said.

Since that first canoe trip, Heron has taken thousands of photographs of wildflowers, water spilling over rocks and people enjoying the river. Many of his photos have appeared in the association's calendar, printed since 1972, and several are in the 2007 edition.

The association began protecting land through the Nature Conservancy, a national organization, which enabled landowners and others to get tax credits for donations, said Don Cox, an Orange County resident who serves on the Eno River Association board of directors.

The donation that really got things going came from the Nygards' neighbors, Molly and Frederick Bernheim, biochemists and members of the original faculty of the Duke School of Medicine. The 90 acres known as the Cabe Lands, including the West Point Mill site, became a Durham city park when the city decided to build a reservoir on Little River instead.

The state, too, came around to the idea of a park along the Eno. And the association has helped create that linear park, buying property and accepting land donations, which it has sold to the state to create the park master plan.

"We all felt extremely fortunate that it turned out as it did. Back in the beginning, there was not a good history of grass-roots efforts combating state or municipal groups and winning," said Jean Anderson, another neighbor of Nygard.

In recent years, the association has turned to protecting land deeper in the Eno River's watershed. But, as many founding members enter their 70s and 80s, they also want to see a continued emphasis on educating those who will follow them.

"That will be so important, to continue letting people know how important the river is in its natural state," Cox said. "Because there will be times in the coming decades that there will need to be a constituency for the river, and a lot of us won't be here then. But our grandchildren will."