When our new baseball stadium gets built on the Anacostia River, colorful flags will fly from the ramparts -- pennants of other National League teams, the District flag, Old Glory itself, maybe one day even a division or league or World Series championship banner.

What a fine spectacle that will be. Meantime, a few flags already fly along the Anacostia, but nobody wants to see them because they bear a much grimmer message.

"See that yellow flag?" asked Robert Boone, president of the Anacostia Watershed Society, who has worked the past 15 years to try to clean up the Potomac's filthy feeder. He pointed across the water to a flagpole above the Earth Conservation Corps' riverfront headquarters, just a few hundred yards from the spot where one day soon umpires will shout, "Play ball!"

The butter-colored banner fluttering there, and others at nearby Matthew Henson Environmental Center and the Anacostia Community Boathouse, signaled that on that particular day, the fecal coliform count in the river exceeded the recommended level for human contact. Fecal coliform is the scientific term for poop. The flag was to warn folks to stay away.

That was on Wednesday, when all Washington waited giddily for the call to come from Major League Baseball commissioner Bud Selig announcing the long wait was over and after 33 years we were back in the big leagues with a team, manager, coaches and a brand new stadium to be built -- overlooking an open, stinking sewer.

"When they flushed the toilet at the White House yesterday," said Lawrence Silverman, an environmental lawyer who was along for our boat ride past the new stadium site, "this is where it came out."

Ah, the affluent effluent . . . Most people in Washington don't know the sad story of the Anacostia, the scenic, sluggish tidal river that flows from Bladensburg to Hains Point. They know it's a mess, but they don't know why.

Here's why: Washington's antiquated sewer system, which dates from the 1800s, combines stormwater runoff and sanitary sewage in the same pipes. Everything flows to Blue Plains, the city's modern and efficient sewer plant near Oxon Hill, for treatment.

It all works out fine except when there's heavy rain, when the pipes can't handle the flow and huge slugs of combined street runoff and raw sewage are diverted, most of it directly into the Anacostia.

The upshot is that every time there's more than a half-inch of rain -- about 75 times a year, according to Boone -- the Anacostia runs murky brown and digests an environmental insult of massive proportions. Up go the yellow flags.

Environmentalists like Boone and Silverman hope the decision to bring baseball to the Anacostia's banks will benefit the river. The industrial site on the river's west bank where the stadium will go has no redeeming aesthetic or environmental value, they say, and the project could be a plus if done properly, with vegetated buffers along the banks, trees, walkways and an environmentally sensitive design for the parking lots.

Moreover, if baseball draws thousands of people to the Anacostia who find a fetid sewer when they get there, maybe the government finally will be shamed into fixing the problem.

We putt-putted upriver on a pontoon boat discussing the matter along with Jim Connolly, the AWS's executive director, and Dianne Dale, a longtime member of the Anacostia Garden Club and head of Frederick Douglass Gardens, a group that aims to build a memorial to the 19th-century African-American hero across the river from the proposed ballpark in Anacostia Park.

Dale thinks spending $440 million on a baseball stadium is a stupid waste of public money, but she said she wouldn't oppose the plan. She is, however, dead set against putting a soccer stadium across the river, right where her Douglass Memorial is supposed to go. The 1,200-acre national park is a place for people to rest and reflect, she said, not for a private, for-profit soccer stadium.

Dale has lived in Anacostia all her life and said as bad as the river is today, it was worse in her childhood, when "nobody went near it." Pressure from community organizations over the last 20 years pushed the District and Prince George's County to upgrade sewer maintenance and stormwater management. That, along with volunteer river cleanups, made the Anacostia and its adjoining park a reasonably pleasant place to go on good days, complete with ospreys, herons, ducks, geese and fish, none of which she saw in the old days.

Nowadays, some people even regularly get out on the river. Connolly, a recreational rower, said the Community Boathouse puts 200 boaters a day on the water, many of whom go even if yellow warning flags are flying. He does so himself. "You just have to be careful and wash up when you're done," he said. "I do get infections on my hands and arms."

What a sorry state of affairs, here in the capital of the richest nation on earth.

Five years ago, AWS and a handful of other environmental groups sued the D.C. Water and Sewer Authority over the Anacostia sewage spills, said Boone, and later the Environmental Protection Agency took over the litigation.

The suit is still in play, and $140 million has been approved to boost sewer pumping capacity and make other improvements that should reduce sewage coming into the river by about 40 percent, he said.

But it would cost another $1.2 billion to build underground holding space to handle the storm surges. It sounds like a lot but other cities, notably New York, Chicago, Milwaukee and Boston have made the sacrifice, Boone said.

Maybe all the hoopla over baseball will spill over into an environmental movement and some good will come of it. "We'll get some crumbs," Silverman said. "The question is, will we get a seat at the table for the main course?"

Robert Boone and Dianne Dale hope a baseball stadium will improve the Anacostia River.