The blemished underbelly of a key environmental policy has been exposed in Fairfax County.

Streams feeding into Chesapeake Bay are protected by sound scientific and legal regimens to shield them from contamination -- except when it conflicts with development interests. An extensive, science-based process defines which streams should be protected. A comprehensive legal framework ensures that development avoids these streams. But Fairfax County officials recently confirmed that this protection can be removed irreversibly and without public input at the behest of developers using only "eyeball" evidence. As a stream ecologist and an environmental lawyer, respectively, we are greatly concerned about this lack of parity and its potential consequences for the bay.

The Chesapeake Bay's value to our region is enormous, but this precious jewel is in peril. Blue crab landings are near historic lows. Oyster harvests are about 1 percent of historic levels. Sea grasses cover less than half their historic area. And red tides regularly choke the oxygen out of the water.

Twenty years ago, the U.S. Environmental Protection Agency attributed the bay's decline primarily to contaminated suburban runoff. This peril has not abated. Impervious surfaces rapidly shunt dirty water into streams. Stream-side vegetation, once removed, can no longer filter runoff. The lesson learned is that the best way to protect the bay is to protect headwater streams throughout the watershed.

Virginia took heed by participating in the historic interstate Chesapeake Bay agreement and requiring tidewater counties to identify environmentally sensitive buffer areas along perennial waterways, which cannot be disturbed by development. Fairfax County uses an exceptionally robust protocol to identify which streams to protect, relying on 26 hydrological, physical and biological characteristics that decades of scientific inquiry have shown mark the critical features of a perennial stream.

The reason for this multi-factored analysis is that water moves through the sediments of a streambed even when it is not visible. This flowing water, often less than an inch out of sight, supports aquatic life and can certainly carry pollutants toward the bay. A number of the protocol's 26 factors can signal the likely presence of such below-streambed flow: seeps and springs, for example, or aquatic creatures that require running water to live. Flowing streams also write their signatures on the landscape, as meandering channels with a sequence of riffles and pools. The protocol accordingly cautions that visual "flow may stop at a point and begin again some distance downstream," and the simple observation of flow by human eyes or lack thereof is not determinative. In other words, appearances can be deceiving.

But despite the scientifically rigorous protocol and state regulations requiring "a reliable, site-specific evaluation" before stripping protected streams of their buffers, Fairfax County permits the elimination of stream buffers in developing areas based simply on visual observations of a purportedly "dry" stream. Regrettably, such evidence may be submitted by individuals with a financial interest in the property. Citizens have no role to play in the process, no ability to appeal a decision, and, worst of all, cannot trigger a renewed evaluation of a stream. At some unforeseen time, the county may revisit the issue, but otherwise a stream declassification is permanent.

We learned about this because of a stream declassification on the Wedderburn property in Vienna. In 2003, qualified and neutral county staff applied the protocol and concluded that the stream should be protected. "It's a very good looking stream," staff wrote, "[d]efinitely perennial." But the county declassified this "definitely perennial" stream last fall -- without public notice -- based on photographs of a "dry" stream on two days during a week when U.S. Geological Survey data show that all local stream flow was at a two-year low. The other 25 factors of the protocol were ignored and the stream's buffer was eliminated, but only on the property subject to development. Once the stream leaves the property, it is, miraculously, perennial, as confirmed by the developer's own consultant.

While the fate of the Wedderburn stream alone will not exacerbate the record dead zones predicted for the Chesapeake this year, similar streams across Fairfax are at risk, and the cumulative threat is profound. Although the county is now considering amending some of its declassification rules, the amendments still allow exclusive reliance on visual evidence of stream flow and will not consider subsurface flow that may continue despite a temporarily "dry" appearance. And, as we have learned directly from the director of the Department of Public Works and Environmental Services, the county will not allow a restudy of the Wedderburn stream to reverse the prior declassification, even if citizens conduct and pay for a new protocol review.

Certainly the first time that Fairfax County declassifies a perennial stream -- which this is -- should be subject to a second look to ensure it is done right. Measure twice, cut once. Otherwise, the careful system of interstate protections to rehabilitate the imperiled Chesapeake Bay will suffer the death of a thousand paper cuts. As the streams go, so goes the bay.

Firth is a stream ecologist. Reyher is a senior lawyer in the environmental enforcement section of the Department of Justice, but her views in this column are her own.

A McLean developer's plan to build a residential community on a 13-acre parcel known as the Wedderburn property in Vienna has created tension among nearby residents. Among other things, opponents are concerned about the county's declassification of a stream on the property, which stripped it of protection under the county's Chesapeake Bay preservation ordinance. In the June 23 Fairfax Extra, one of the developers explained his position ["Stream 'Lost' Nothing in Development Plan"]. Today, two environmental specialists, Penelope Firth and Deborah Reyher, offer a different view.