A Filmmaker's Watershed Productions

"When I learned that the water from my house went there . . . and now is part of the problem that's destroying it, I said, 'Well, I have no choice,' " Eckert recalled.

"I think their intention was to have a beautiful movie, make people love the Dyke Marsh and that's it. That's a great thing, but that's not generally enough," he said.

It didn't take long to find the hook. The 5,000- to 7,000-year-old marsh has shrunk by more than 40 percent since dredging began there in the 1930s. Although those operations ended in the 1970s, Eckert said other potential threats -- such as storms and rising water levels from global warming and invasive plants introduced by humans -- make what is left vulnerable.

As Eckert and members of the volunteer group poked around the marsh one morning last month, it was obvious that Eckert had embraced it as whole-heartedly as he had the subjects of his other films.

Even in early spring, before the marsh had blossomed with the myriad colors of late spring and summer, he grew excited at signs of the still-thriving but threatened ecosystem.

Eckert radiates enthusiasm when he talks to audiences about the film, said Flo Stone, artistic director and founder of the Environmental Film Festival in the District. Each year the festival presents about 100 documentaries from nearly two dozen countries. Stone said that she has been impressed with Eckert's films and that they add a local element to the festival.

"We felt so lucky when he got hold of the festival five years ago," Stone said. "He is really focused on local issues that have relevance elsewhere." More than 400 people were at the marsh film's debut at the Kennedy Center in March, Stone said.

Since he completed "On the Edge," Eckert has busied himself with another film-related project. He created the Falls Church Film Festival, which featured the Dyke Marsh film and five other short documentaries from filmmakers who live in the 2.2-square-mile city. The movies were screened at the State Theatre last month, and Eckert said people have already been asking him to put on the festival again next year.

Whether a new film of his own will be among the offerings remains to be seen. But if the past is any indication, the demand for his work won't disappear.

"I'm very concerned with our ability to sustain ourselves; for the human race to sustain itself," he said. "And there are so many different aspects. Whether it's the environmental aspects that sustain us or the cultural aspects that sustain us -- I have a deep interest in that. To make films is really just a medium I happen to work in."