You've heard about wars on crime and drugs; now comes the war on impervious surfaces. The aim is to save the Anacostia, Washington's forgotten river out the back door.

Compared to its front-yard sister, the Anacostia is a mess. In the Potomac, aquatic grasses proliferate, the water is relatively clear and largemouth bass, striped bass, bluegills, perch, waterfowl, shore birds and other higher life abound.

But hang a right where the waterways join at Hains Point and almost instantly you enter a silted wasteland of mud, stench, murk, trash and sparse aquatic life -- the Anacostia. Though they meet, these are very different rivers.

The reason is simple. The Potomac flows through miles of forests and fields before finding the city, arriving relatively clean. Thus, a $1 billion federal cleanup over the last 20 years could be aimed almost exclusively at upgrading local sewage treatment. It worked, making the Potomac one of the healthiest urban rivers in the nation.

The far smaller Anacostia, by contrast, is the hapless victim of urban blight. Its 165-square-mile watershed is the highly developed land that surrounds the Nation's Capital. When it rains hard, torrents of water sluice into the creeks and down to the Anacostia from filthy, overheated concrete and asphalt, from roofs and gutters, junkyards and parking lots.

A Montgomery County tributary, Wheaton Branch, is a good example. It's narrow enough to jump across yet it drains an area that's 55 percent impervious surface, including Georgia Avenue and the huge, funk-encrusted parking lot at Wheaton Plaza. Imagine the clots of oil, trash and crud that roared through Wheaton Branch during last weekend's gullywashing thunderstorm.

For years, the damage from such events went unmeasured, but no more. In a healthy Wheaton Branch, "We'd expect to see 50 types of fish," said John Valli of the Metropolitan Area Council of Governments, "but when we surveyed there we found only two -- black-nosed daice and creek chubs."

His survey is part of a major effort by a coalition of government agencies -- COG, Prince George's and Montgomery counties, Maryland, the District, the U.S. Environmental Protection Agency and the Corps of Engineers -- to set the Anacostia and its filthy feeders right.

The plan calls for making the river and tributaries fit for fishing, boating and swimming in 10 years, a goal so ambitious no one is at all sure it's within reach.

"If restoration succeeds here," said Lewis Linker of EPA, gesturing at a fetid Anacostia mudbank at low tide, "we'll know we can turn it around anywhere" in the Chesapeake system.

"But the jury is still out," he said. "We've seen Great Lakes turned around, the Potomac turned around. But what about an urban watershed? No one knows. That's why EPA is involved, why we're interested."

Initial steps already have begun in the $50 million cleanup and last week COG hired a couple of Ride-On buses to squire interested folks around to see the changes. It was an eye-opener.

Across the region, local officials are doing about-faces, trying to undo the destructive practices of their predecessors.

Where 20 or 30 years ago concrete watercourses were installed to speed floodwaters out of developments, today costly obstructions and holding areas are being retrofitted to hold the water back so it can deposit silt, energy, nutrients and pollutants before they get downstream.

Where trees were bulldozed to clear a path for water to run, trees are being replanted along creek beds; where marshes were filled and channels straightened, marshes and meanders are being restored.

Storm water management ponds are being carved into a crowded suburban landscape. Montgomery County spent $700,000 of its money and $100,000 in state funds on a trio of ponds off Dennis Avenue in Silver Spring to benefit Wheaton Creek.

In Prince George's, 117 storm water management projects have been approved "to make up for prior mistakes" on feeder creeks, said County Executive Parris Glendening.

In the District, a $14 million "swirl concentrator" is ready to begin treating combined sewage overflows of up to 400 million gallons a day that used to flush straight into the Anacostia during storms.

The general idea is to slow the flow, restoring to creeks or their technological replacements the role of filtering pollution and holding back some water during the sort of sudden storms that occur here up to 100 times a year.

What officials are finding, said Tom Schueler, chief of COG's Anacostia restoration team, "is that it costs a lot more to fix things after we screwed them up than if we did it right in the first place."

But, he said, "It's only recently that people made the connection between impervious surfaces and aquatic degradation.

"You've seen the joke bumper stickers, 'Pave the Bay.' Well, we've already done it. There's more paved surface in the Chesapeake drainage area now than the surface area of the Bay itself, and in the next 25 years that would double if current population growth figures are accurate."

Which, said Schueler, means the Anacostia today "is a vision of what the Chesapeake Bay could be like in 100 or 200 years if we don't learn how to control growth."

A chilling thought, that, and worth going to war to prevent.