In mid-August, when river advocates gathered on the banks of the Rivanna River to announce the ongoing breaching of the Woolen Mills dam, they heard something unknown for nearly two centuries.

The summer drought had been broken by rain the previous night, raising the level of the river through Charlottesville; the Rivanna was flowing freely through a portion of the breach.

"That was probably the first time in 177 years that you could hear the river there," said Jason Halbert, a volunteer with the Rivanna Conservation Society who had been working to remove the dam for six years.

In the next few weeks, most of the rest of the dam was removed, opening the James River tributary to migratory fish, and clearing the way for kayakers and canoeists. "The eels are already loving it," Halbert said.

A rarity until a few years ago, such dam removals are becoming commonplace around the region as biologists seek to open historic spawning areas for migratory fish and help return streams to a more natural condition.

State and federal agencies, national conservation groups and grass-roots organizations such as the Rivanna group, now champion removing dams where possible over the historic emphasis on constructing fishways.

They have a daunting task: In past centuries, dams were built by the thousands. First, they provided power for the Industrial Revolution, running mills and providing water to a vast network of canals. Later, they provided electricity, city water supplies, flood prevention, recreation and a host of other services.

The Bay watershed alone has more than 2,500 dams, shutting most of the watershed to spawning runs of shad, herring and other migratory species that once numbered in the millions.

Nonetheless, the pace of removals is quickening. This was the first year in which Pennsylvania, Maryland and Virginia each removed multiple dams.

Some of this year's highlights include:

  • In Pennsylvania, the McCoy-Linn Dam, an aging 14-foot, 150-foot-long structure in Centre County was removed in August. A related project will restore roughly a mile of high quality habitat at the site to help make it a recreational destination. "It is on, arguably, the best wild trout stream in the commonwealth, and there is a significant amount of habitat that is going to be opened up and created for the trout population there," said Dave Kristine, of the Pennsylvania Fish and Boat Commission.

    Also in Pennsylvania, the Wittlinger Dam on the Yellow Breeches Creek near Boiling Springs was removed. The dam, about 4 feet high and 90 feet long, had been damaged in several storms in recent years and become a hazard.

  • In Maryland, a 4-foot-high earthen dam was removed on the Puckum Branch of the Nanticoke River in January, opening 4.5 miles to alewife, blueback herring and perch.

    This fall, officials were planning to remove the Pittsburgh Plate & Glass Dam, an old pile of rubble across the Potomac River near Cumberland, MD. They were also planning to remove the Raven Rock dam, a concrete and mortar barrier to brook trout movement on Raven Rock Creek near Hagerstown.

    "We're definitely looking for removals rather than ladders," added Jim Thompson, fish passage coordinator with the Maryland Department of Natural Resources. "We have a bunch queued up for next year."

  • In Virginia, the Quinn Dam on the Tye River, a 6-foot-high blockage on the James tributary near Lynchburg, was also removed, opening 20 miles of habitat to migratory fish.

    "Local canoeists and people around the state are also pretty excited because it's a popular river to canoe, and the dam has always been a problem," said Alan Weaver, fish passage coordinator with the Virginia Department of Game and Inland Fisheries.

    Reopening those rivers has been a Bay Program priority since 1988. But for years, more emphasis had been placed on building fish ladders or other passages. Giant elevators were even built at some dams on the Susquehanna River to hoist shad and other species over the obstructions.

    While those passages theoretically opened more than 2,100 miles of Bay tributaries to migratory fish, biologists have often been disappointed by their performance.

    On the Susquehanna River this year, 25,464 American shad were lifted over the Conowingo Dam-the first obstruction on the river. But only 192 made it past all four hydroelectric dams in the first 80 miles of the river to reach spawning habitat.

    Such problems highlight that even the best designed passages can still pose significant hurdles for fish.

    In contrast, Weaver said, dam removal is "basically 100 percent effective at fish passage."

    More than migratory fish benefit. Dams fragment, and degrade, habitat needed for local fish, such as brook trout.

    When the Reedsville Dam was removed on Tea Creek in Pennsylvania's Mifflin County in 2004, the biomass of brook trout doubled within a year, Kristine said. The population has since continued to expand.

    The move toward dam removal was dramatically punctuated in February 2004 when 650 pounds of explosives were used to begin breaching Embrey Dam on the Rappahannock River outside Fredericksburg, VA. Until the 22-foot-high, 770-foot dam was breached, there were no free-flowing rivers that linked the Bay with its mountain headwaters.

    The next year, the Bay Program adopted a policy promoting dam removals over passages where practicable.

    Pennsylvania already had an aggressive program to remove dams-it has removed more than 70 dams in recent years, more than any other state. Since Embrey, removal activity has stepped up in Maryland and Virginia as well.

    None of this year's projects were as large or dramatic as Embrey, or opens hundreds of miles of habitat.

    The largest dam removed this year, Woolen Mills, opened 16 miles, but biologists say the bits and pieces add up. "More habitat, more fish is our philosophy and seems to be a good way to look at it," Weaver said.

    The state stocked several million shad larvae above the dam in recent years in the hope that after they migrate to the ocean, they will return to their native river and spawn when they mature at age 4 or 5.

    Loss of access to habitat is one of the reasons cited for the declines of shad, eels and other migratory species.

    But removals serve other purposes. Because of their age, the driving force behind many dam removals are deteriorating conditions and their potential hazard to public safety.

    Some people wanted to preserve the Woolen Mills dam because it was a historic structure, built in 1830 to power a mill and also serve as part of a series of dams, locks and canals that allowed boats to travel up the river. The Woolen Mills company manufactured wool uniforms until it closed in 1964, although it had switched to electric power around 1900.

    But a swimmer was killed in 2003 when he was swept over the top. Ultimately, no one wanted to absorb the liability for the structure. "That wasn't practical at all," Halbert said. "The cost to repair the dam would have been tremendous, and that would not have removed the hazard."

    As part of the agreement to remove the dam, about one-quarter of the 300-foot-long dam was left standing. Portions of the adjacent canal system are also being preserved. A kiosk will be built to interpret the historical significance of the site.

    Halbert said the dam removal exposed a scenic "rock garden" that had long been hidden by the structure. He said the removal-coupled with planned improvements at parks along the river and the potential for a canoe livery in the area-should increase public appreciation for the Rivanna. "It's the kind of thing where I hope the community comes down to the river more now that the dam is gone," he said.