Remember hydrilla, the dreaded weed that was going to eat the Potomac?

Maryland's Department of Natural Resources moved today to do something about it, but hydrilla-haters will be disappointed to learn that what DNR wants to do is protect the noxious underwater weed from uncontrolled harvesting.

The state agency is backing a bill to control mowing of growing patches of the submerged grass in the Potomac. Such mowing took place last summer by citizens because hydrilla was choking some shallow areas, washing up on beaches and making boating difficult, particularly around Wilson Bridge on the Potomac within sight of the Washington Monument.

But hydrilla can be beneficial, too, Will C. Baker of the Chesapeake Bay Foundation said today. "Hydrilla does the same things" all aquatic grasses do, said Baker, who backed the proposed controls at a hearing before the House Environmental Matters Committee.

"It buffers against erosion, screens sediments, reoxygenates and clarifies the water and serves as habitat for aquatic species and as food for waterfowl."

DNR Secretary Torrey Brown said his agency's studies showed that in some areas of the Potomac where the civic groups intended to cut hydrilla, what they in fact chopped down was 10 percent hydrilla and 90 percent "other, officially good grasses."

Brown, who testified before the committee, said the citizen attacks on such grasses are hard to endorse when his department, as part of the statewide Chesapeake Bay cleanup initiatives, is trying to get grasses to come back to the bay region.

Brown also said he believes concern about hydrilla "is exaggerated. I seriously doubt hydrilla is going to take over the river or the bay, and we find that in areas where hydrilla is growing, other grasses are coming back, too."

Frank Dawson, a DNR biologist who accompanied civic-minded hydrilla mowers on the Potomac last year, said analysis of their catch turned up mostly water star grass and naiads, plus milfoil, wild celery, coontail grass and hydrilla.

Hydrilla, a rapidly spreading grass that has choked ponds and shallow waterways in Florida and other southern states, was introduced into the Potomac several years ago in an experiment.

It spread quickly in some areas, and by last summer was regarded as a nuisance around Belle Haven Marina, where it interfered with boating.

The bill would allow small-scale clearing of grass around docks, boat moorings, beaches and swimming areas. Channels could be cleared, though advance notification of DNR would be required. For any larger clearing project, DNR approval of the plans would be required.

Dawson said aquatic grasses are staging comebacks in the Chester River, along the Susquehanna Flats and in other bay areas, as well as the Potomac. He hopes to expand the range this summer when he begins transplanting grasses in areas denuded over the last decade.

Without the mowing restrictions, he said, "We could be in a situation where as fast as we plant it, somebody else would be taking it up."