Centennial Lake is one of Howard County's most prized amenities. Each year, the lake and the park that surrounds it attract some 1.5 million visitors, who flock there to stroll its paths, paddle a canoe on its waters or fish from its shores.

But the 15-year-old lake isn't aging well. Clogged with silt from runoff and erosion, that lake and another Howard County focal point, Lake Kittamaqundi in Columbia, need expensive dredging and repairs to restore them to their former health. The lakes, built to be glimmering recreational centerpieces for the growing county between Washington and Baltimore, may be a dying breed.

"Centennial Lake is probably going to be our one and final entry into large, man-made lakes," said county Recreation and Parks Director Gary J. Arthur. "We're just not prepared to do it anymore."

County officials say the cost of maintaining the lakes has led them to scrap plans for a lake at the proposed Western Regional Park and to put on hold plans for another at Rockburn Branch Park.

The problem, he and other officials said, is that as the county continues to develop, and as subdivisions replace farmland and forests, there are fewer trees and less grass and foliage to capture and absorb sediment that is washed away by storms. Instead, the sediment runs off pavement and down stream beds and into lakes--chipping away at their edges, piling up in their basins and choking the life out of them.

Silt, a fancy word for gunk that could contain topsoil, fertilizer, animal waste and whatever else runs off the land, piles up in lakes and streams just about everywhere. In many places, it kills fish that need oxygen-rich water to survive. In Howard County, the silted lakes lie in the watershed of the Little Patuxent River. "All the development we see upstream of it, some of it in Columbia, most of it up toward Ellicott City, has accelerated erosion problems," said Charles "Chick" Rhodehamel, director of Columbia Association's open space management.

It's not all development's fault, of course. Runoff from farmland contributes, too, and erosion is a process that occurs in nature anyway.

"It's a case of degree," said state Department of Natural Resources biologist Nick Carter. "What development does is simply speed it up."

According to a 1995 study, 52-acre Centennial Lake has lost 14 percent to 17 percent of its volume to sediment buildup. The murky water is still, and occasionally, one can detect the pungent odor of algae. Parks officials already have spent $25,000 to study the silt problem there, and they plan to spend $385,000 in 2002 to fix it.

The costly restoration won't be a one-time shot. "We see that this is going to be an ongoing process," Arthur said. A consultant is studying how best to dredge the lake and stabilize its shoreline, and Arthur expects the report in the spring.

A few years ago, it took more than $500,000 to transform a badly silted two-acre pond in Ellicott City into a wetlands park. Sediment had swallowed nearly half the volume of the little pond at Font Hill Park, so the county, with help from a few area developers, drained it, rebuilt it and planted vegetation around it.

Nearby at Lake Kittamaqundi, where residents rent paddle boats and linger along a dock in Columbia's Town Center, algae floats on the water. Areas near the shore are marshy and becoming more overgrown. Columbia Association, the nonprofit homeowners group that maintains the lake, has asked the county to help pay to remove the silt and fix a larger problem.

About 60 years ago, the channel of the nearby Little Patuxent River was widened and straightened to help keep surrounding low-lying areas dry, Rhodehamel said. That slowed the water flow, allowing more silt to build up and eventually causing the river to spill over its banks more frequently. When it does, the overflow, silt and all, heads for Lake Kittamaqundi, which lies in the river's flood plain.

"If we don't do something, the northern end of the lake . . . will begin to fill itself in pretty significantly," Rhodehamel said. "It'll become a marsh and ultimately proceed back to dry land."

These days, residents cram the lakefront for summer concerts, arts festivals and Independence Day and New Year's celebrations, and popular restaurants such as Clyde's feature walls of windows overlooking the lake. County Executive James N. Robey (D), according to his assistant, Herman Charity, is "interested in helping to try to find some resources to help fund the project, hopefully through state or federal grants."

Columbia officials want to remove the silt from the lake and restore the river channel to its winding ways.

"Since one causes the other, you can't just scoop out the sediment and say, 'Well, that's done,' " Rhodehamel said.

Environmentalists say slowing development would help slow erosion. "We're worried about the nutrients that are being dumped into those [lakes] and ending up in the Chesapeake Bay," said Dennis Luck, chairman of the county's Sierra Club chapter.

"Sooner or later, you just come up against the fact that maybe you shouldn't develop a certain area if you don't want to deal with the associated problems," said the Department of Natural Resources' Carter.

Otherwise, for fast-growing places such as Howard, Arthur said, "I guess if we get 14 or 15 years out of a lake, it's not that bad."

CAPTION: Peggy Desautelle and her sons, Scott, 3, left, and Culloty, 2, feed the ducks, sea gulls and geese on the shore of Centennial Lake.

CAPTION: Pink ribbons mark spots around the Howard County lake where surveyors have measured the inflow of silt by satellite.