The suburban street looks like many others: neat ranchers with garages in front and yards that look freshly mowed. At the end of the block sits a community of newish homes built in the 1980s and 1990s when western Baltimore County was growing quickly.

The bridge from the older homes to newer ones is almost imperceptible. But visitors who look behind the guardrail in this Gwynn Oak neighborhood will see a stream peeking out of the weed-choked woods. Walk a little farther, and the stream enters a concrete tunnel nearly a quarter-mile long.

Like so many streams in suburban Baltimore and Washington, DC, this one is buried. It has no name. Children don't play in it. Adults don't think about it much, other than to monitor it to make sure it doesn't cause flooding. The only hint of its existence is in the name of the roadway: Glen Spring.

For decades, as cities and counties became urbanized, planners focused on getting rain water away from homes. In Baltimore and Washington, where hundreds of small creeks and streams feed the Chesapeake Bay, that usually meant channelizing, paving and ditching the waterways. Nobody really missed them. But the minnows, worms, frogs and microorganisms that called them home and broke down the stormwater's organic material could no longer survive once the streams became concrete.

As a result, the buried and channelized streams deliver higher levels of nitrogen, phosphorus and carbon to larger rivers and the Bay, according to research by University of Maryland professors Sujay Kaushal and Andrew Elmore.

A big part of the problem, Kaushal said, is that the buried streams are connected to both the sewer system and the storm drains. Kaushal and Elmore's 2008 paper in Frontiers in Ecology and the Environment introduced an algorithm to map each stream in the Baltimore area and review its status.

Both scientists are continuing their work on buried streams. Kaushal is testing buried and unburied streams to determine how much more nitrogen and phosphorus enters larger rivers when the tributary streambed is concrete. Elmore is mapping all of the buried streams in Maryland west of the Chesapeake Bay and all of those in the Potomac River watershed. That includes all of the District of Columbia and parts of West Virginia, Virginia and Pennsylvania.

One positive development, Elmore said, is that cities and towns are realizing that burying waterways is a bad idea — not only because buried streams deposit more pollution into the larger waterways they empty into, but also because babbling brooks and free-flowing rivers are far more attractive than blocks of concrete.

"There's something we call pipe creep. You've already buried part of it, and you want to get a permit to bury it a bit more, extend it another 10 feet. That still goes on. But wholesale stream burial, the way Baltimore has done in the Jones Falls, as an example, that doesn't really happen anymore," said Elmore, a landscape ecologist at the University of Maryland's Appalachian Lab in Frostburg.

Montgomery County is a good example, Elmore said. Although county engineers buried and channelized many streams when the county was developing in the 1970s and 1980s, it is now focused on restoring the streams, and a big part of that is uncovering them, or "daylighting" them.

Baltimore officials have discussed replacing the Jones Falls Expressway, which in places covers the Jones Falls, with a boulevard that would daylight some of that stream. In Washington, DC, officials are discussing removing some of the highways that run through parks and now bury or channelize parts of the Potomac and Anacostia rivers and their feeder streams.

Brent Bolin, director of advocacy for the Anacostia Watershed Society, said DC has begun a lot of these projects. One detail making it easier to do them, he said, is the large amount of land owned by the National Park Service or the Maryland National Capital Park and Planning Commission. It remains difficult and expensive to daylight whole streams, Bolin said, because that often requires road removal and the permission of multiple agencies. But in recent years, he said, the Park Service and the commission have been amenable to removing the channels and hard surfaces to restore the streams to a more natural state in areas where it's possible to do so and still protect neighborhoods from flooding.

"I understand having to channelize a stream under a roadway, but there is sometimes another half-mile that's been channelized. That tributary is now going to be a biological dead zone…when we stock shad, there are whole zones we cannot reach because of those barriers," Bolin said

In Baltimore and the surrounding counties, stream restoration has been on a project-by-project basis.

In 2009, Baltimore city restored Stony Run, a popular hiking area near the city-county line. Baltimore County has daylighted several streams, including one across from the Timonium Fairgrounds off York Road. Ecotone, a Harford County firm, is preparing to expose Plumtree Run, a stream that was buried in the 1950s when the area was developed. The town of Bel Air and the Harford County Conservation District will collaborate on that project.

Kaushal said he's pleased to see these projects, and he agrees with Elmore that municipal planners are far more aware of the damage done when streams are buried than they were a decade ago. But, he said, there is still too much out-of-sight, out-of-mind when it comes to stormwater management.

In the case of Glen Spring, Kaushal said, maybe the planners did the best they could with what they knew. But now, years after the last house was built, they know better.

"We need to realize that infrastructure evolves over time," he said. "Just because we built a neighborhood doesn't mean it's done."