You’re a blueback herring slinking about the Potomac River in early spring. As you munch on plankton and fraternize with your own kind, you’re struck by the innate need to spawn in your ancestral waters. So you take a right onto Rock Creek.

Bad move.

At first, you’ll have no trouble as you fight the current past the creek’s main downstream landmarks, like the overpasses at P and Q Streets and the pedestrian bridges for park users. You may get a bit disoriented as you wend through the curves by Connecticut and Calvert. But, hey, you’re spawning, fer chrissakes: Nothing will stop you.

Until you hit the bend by the National Zoo. There you’ll ram into a big concrete slab. Poke and prod all you want, but there’s no breach in this wall. Cross your fins in hopes that the water level rises enough to get over it. If you manage to get by, remember how you did it, because there’s another slab just ahead. Word among spawners is to try the right end of the slab, where the roadblock dips a bit.

If that works, keep swimming. Stretch out. Work your stroke. After all, your spawning outing won’t last much longer: The Pierce Mill dam is just ahead.

Man has orchestrated a century-long conspiracy to keep the blueback and alewife herring species from plying Rock Creek on their annual spawning runs. Each spring, thousands of the foot-long fish congregate in impromptu schools in front of the creek’s various obstacles, their instinctive urges stonewalled. Absent the roadblocks, the fish would dart their way up the 12 to 15 miles of fertile spawning turf upstream. Each fish would lay hundreds of thousands of eggs, replenishing a species in steady decline. “We’ve reduced the herring population in Rock Creek by at least 75 percent since the turn of the century,” says Ira Palmer, chief of the city’s fisheries and wildlife division.

The disruption might be excusable if the obstacles served a higher good for humans or wildlife. They don’t.

Maarten Sengers, a downtown lawyer, pays more attention than most to the critters in Rock Creek. On a bike ride home last April, he spotted a heady upstream migration of herring. “It was tax day, so I was filled with tax angst, and the fish were a soothing distraction,” says Sengers, who added that he was “having a ball” watching the fish pass under the bridges.

Once Sengers passed the zoo, however, the party was over. “It was like a desert,” says Sengers.

The concrete slabs that the herring encounter by the zoo are fords that carried traffic across the creek before 1966, when the current roadway was constructed. They now serve no function other than to stymie migratory fish. If the little creatures are lucky, says Bob Ford, Rock Creek Park’s resource manager, “they can wiggle on their sides and flop their way through.”

“If the fish can’t get up to their natural spawning habitat, they’re handicapped,” says Jim Cummins, a biologist with the Interstate Commission on the Potomac River Basin.

Although the fords lie on property of the National Zoo, their removal is not a priority for zoo officials. Friends of the National Zoo Executive Director Clint Fields was unfamiliar with the migratory obstacles and referred questions to zoo spokesperson Bob Hoage. “I can’t tell you a whole lot, because I don’t know a whole lot,” says Hoage.

The zoo apparently sees no crisis in having a few more caged animals on its grounds.

In fairness to the zoo, however, migratory herring stir about as much interest among local environmentalists as rats and pigeons. “We’re concerned about human health issues such as drinking water, the swimmability of our rivers, and natural resources that if lost are irreplaceable, like Children’s Island and other riverfront park land,” says Jim Dougherty, a spokesperson for the local Sierra Club chapter. Dougherty says he has heard of the herring’s plight but acknowledges that the Sierra Club hasn’t addressed it.

That leaves Palmer swimming against the current. As the District’s fisheries chief, Palmer is responsible for bringing Rock Creek into compliance with the 1987 Chesapeake Bay Agreement, which commits participating states to “provide for fish passage at dams, and to remove stream blockages wherever necessary.” It’s necessary just about everywhere: Major rivers and tributaries in each bay state—Maryland, Virginia, and Pennsylvania—are littered with dams, culverts, and sewer lines, which encircle migratory aquatic life like a seine. “Rock Creek’s problems are minor in the context of fish blockage problems in the Chesapeake Bay watershed,” says Palmer.

To do the District’s part under the agreement, Palmer’s crews—with some help from the Interstate Commission on the Potomac River Basin, the Maryland Department of Natural Resources, and the National Park Service, which manages Rock Creek—in 1995 removed two concrete weirs downstream from the zoo. The $70,000 project was funded by the Environmental Protection Agency.

So now the herring’s spawning journey doesn’t end until the fords. Removing them, says Palmer, could cost as much as $50,000—a small price to pay for a new habitat for migratory fish. However, razing the fords invites the same conundrum that bedevils environmentalists throughout the watershed: It would send the fish racing upstream to the next unnegotiable roadblock—in this case, the Pierce Mill dam.

Located just above the Tilden Street crossing, the dam rises eight feet from the herring’s waters. That’s a tough jump even for Air Salmon, but herring are the white men of aquatic gymnastics: They can’t jump.

Beyond stymying migratory fish, the Pierce Mill dam feeds a cute waterfall for cyclists and joggers. Although the structure sidles up to the mill house, it’s too far downstream to supply an intake channel to power the mill wheel. So Friends of Pierce Mill, a booster group of mill enthusiasts, is drawing up plans to dismantle it in favor of a diversionary dam upstream.

The plan makes Friends of Pierce Mill friends of Rock Creek’s herring. Richard Abbott, president of the group, promises that a device to enable fish to get beyond the mill will be built into the new dam. “In any dam we build, we would certainly incorporate a fish passage,” says Abbott. The idea here is to construct an inclined plane with a water flow so that the fish can flop and plod their way upstream.

According to Palmer, a state-of-the-art fish passage could cost up to $200,000, a figure that doesn’t intimidate Abbott. “We are hoping to raise half a million dollars, and we hope that that will be matched by the Park Service,” says Abbott.

Abbott hopes to begin work on the project sometime in the fall, and Palmer says the fords should be gone by spring 1999.

Breakthroughs at the zoo and Pierce Mill would eventually restore a life cycle that has lain fallow since about 1904, when the current dam was erected. The herring’s offspring would frolic in the creek until autumn, when they would head downstream into the Potomac and, ultimately, the ocean. Nature lovers like Sengers would have another migration to follow.

The youngun’s would instinctively remember the chemical makeup of the Rock Creek water in which they were reared—despite all the toxins spawned by runaway development and overpopulation. Three years later, as mature adults, they would return to the same waters to push the cycle onward.

Of course, even that dream scenario is strewn with obstacles. Two sewer lines cross the creek just upstream from the small stone bridge on Beach Drive. “They are big enough to intrude on the stream channel,” says Ford. And if the fishies can plug their noses long enough to get by the sewers, they face a mile-long battle with shallow rapids. “It’s arguable whether the fish could ascend that on their own,” says Ford. “We’ve had fisheries biologists on both sides of that dispute.” Unfortunately, a wrecking ball wouldn’t help them there.CP