A few years ago, biologist Brian Watson was looking for endangered mussels in Virginia’s Rock Island Creek when his assistant went around a bend and made a startling discovery. It wasn’t a rare mussel.
“There’s, like … a stone wall,” she shouted back to Watson. Then added, “That’s a dam.”
Standing 6 feet tall and stretching 55 feet across the creek, the dam was entirely unknown to them — appearing nowhere on maps or dam inventories.
But the dam wasn’t irrelevant to their project: It was taking a toll on mussels, as so many dams do. The biologists found shells of dead James River spinymussels, an endangered species, behind the structure.
“We assumed the mussels probably got washed down to the dam and then died as they got trapped,” said Watson, a mussel specialist for the Virginia Department of Wildlife Resources, noting that the sandy substrate and water depth behind the structure was unsuitable habitat.
It was one of more than 6,500 dams that dot more than 200,000 miles of waterways draining the Chesapeake Bay watershed. That’s an undercount. Many of them don’t appear on dam inventories. Research was required to learn that the one on Rock Island Creek was called the Baber’s Mill Dam, built in the early 1800s.
Large or small, dams create a host of problems. They alter habitat, block fish movement, change water temperatures, promote algal blooms and contribute to the decline of native species. Some are safety threats to people.
But the Baber’s Mill Dam no longer causes such problems.
By chance, an aquatic ecologist from the timber company Weyerhaeuser, which owned the property, contacted Watson about the dam a few months later. The state and company teamed up to remove the structure in April 2024.
Once unusual, such actions are becoming common. During the 1900s, only 56 dams were removed in the Chesapeake Bay watershed, according to Chesapeake Bay Program data — about one every two years. From 2000 through 2025, though, the pace reached about 10 per year, totaling more than 250 removals.
Nationwide, the nonprofit organization American Rivers reported that 100 dams were demolished in 2025 — the fourth highest yearly count on record. But that’s just a fraction of the 558,000 dams estimated to exist. So the organization, which works closely with states on projects, is calling for stepped-up efforts. It set a goal of quickening the pace by 5% — removing 30,000 by 2050, including 4,500 in the Mid-Atlantic.
“We feel really strongly that one of the fastest ways to restore a river and its ecology is by taking out these obsolete structures,” said Adam Schellhammer, American Rivers’ Mid-Atlantic regional director.
Indeed, within weeks of the Baber’s Mill Dam removal, fish that serve as temporary hosts for spinymussel larvae — helping them move around the creek before detaching — were passing through the site. Soon, sea lamprey, a fish that migrates between the ocean and freshwater rivers, were moving by as well.
Migrating toward removals
Dams have been built in the Bay region since colonial days. Their impacts were recognized quickly.
In the 1730s, angry residents on Conestoga Creek in Pennsylvania ripped down a mill dam, blaming it for blocking migrating shad from reaching their upstream nets.
It was a futile gesture. The pace of dam construction only accelerated. Dams powered gristmills and sawmills, and they helped operate canals. Later, they produced electricity, helped with flood control, provided drinking water and created recreational opportunities.
Today, the Bay watershed averages one dam for about every 30 miles of waterways.
Those structures take a toll on fish, especially migratory species targeted by the Bay Program for restoration, such as shad, river herring and eels.
American shad and river herring once supported some of the region’s largest fisheries. They live in the ocean but spawn in freshwater rivers — early settlers relied on spring spawning runs for food after long winters. Now, as much as 90% of East Coast migratory fish habitat is blocked, and populations of those species are near historic lows.
Initially, efforts to help fish focused on building fish ladders. But ladders are often costly, ineffective and designed to benefit only a single species.
Even expensive, complex systems such as fish elevators built on the large hydroelectric dams on the Susquehanna River — at the cost of tens of millions of dollars — have failed to move significant numbers upstream. This year, elevators only moved 4,057 American shad beyond Conowingo Dam on the Susquehanna River. The goal is to get 2 million upstream.
While many dams like Conowingo — a significant hydroelectric facility — still perform important functions, many others have outlasted their purpose.
Until recent decades, the idea of removing outdated dams was not seriously considered. Shannon Boyle, an aquatic biologist with the engineering firm McMillen and co-chair of the Bay Program Fish Passage Workgroup, said the historic mindset was to fix aging dams rather than consider “end of life planning.”
“Most of them are well beyond their design life,” she said. “Usually, they’re designed and constructed to be about 65 years old. The average age on the national inventory of dams is 65 right now. Many of them are 100 years old or more.”
The modern era of dam removal is typically traced to 1999, when the 162-year-old Edwards Dam on the Kennebec River in Maine was demolished because of its impact on Atlantic salmon.
Dam removal was suddenly seen as a key tool to help restore river health and boost populations of migratory fish.
That emphasis was dramatically reinforced in the Bay watershed in February 2004. That’s when the U.S. Army Corps of Engineers used 650 pounds of explosives to begin breaching the 770-foot-wide Embrey Dam on the Rappahannock River near Fredericksburg.
Until it was breached, there were no free-flowing rivers linking the Bay with its mountain headwaters. But within a few years, the numbers of eels detected in Shenandoah National Park, nearly 100 miles upstream, surged. Biologists also began finding American shad and river herring upstream of the dam site.
Today, the Rappahannock is the only Virginia river with an increasing population of shad found in surveys by the Virginia Institute of Marine Science.
“We’re seeing the use of many miles of the upstream habitat that was reopened,” said Alan Weaver, fish passage coordinator with the Virginia Department of Wildlife Resources.
Challenges ahead
Still, there are obstacles to removing the obstacles.
Ray Li, of the U.S. Fish and Wildlife Service and co-chair of the Fish Passage Workgroup, said many of the initial projects were ones with the greatest benefits and willing landowners.
“Those were the easy pickings to restore,” Li said. “Now we’re starting to come up against projects that might be more challenging.”
In many cases, removals can be a long and complicated process. It often takes two to five years to complete design and engineering work, conduct environmental reviews and secure permits. The physical removal, often completed in a few days, is the easiest part.
There is no dedicated state or federal funding for dam removals, and costs vary widely. The average is a few hundred thousand dollars.
Projects are more complex if they affect sewer lines, water lines or roads. Bloede Dam, 10 miles upstream of Baltimore on the Patapsco River, cost $17 million to remove in part because it required relocation of sewer lines and other infrastructure.
The cost can be tens of thousands of dollars less when those problems don’t exist and public agencies conduct some of the design work and, occasionally, the demolition itself. The removal of Baber’s Mill Dam, for instance, cost about $60,000 because the state did much of the preliminary work.
The Bay cleanup itself can pose hurdles. If a project could release a significant amount of sediment, it can complicate state obligations to reduce nutrient and sediment pollution. And it can “balloon the cost” if the sediment has to be hauled off-site, Boyle said. “It can really stymie progress on a project.”
Some dams are so old that identifying owners is problematic, especially when there are different properties on each side. Some dams were deeded separately from properties, and the chain of ownership got lost.
“A lot of people don’t even know they own the dam,” said Jim Thompson, fish passage coordinator with the Maryland Department of Natural Resources. “They know it’s there, but they don’t really know it’s theirs, especially the smaller dams.”
Many owners want to keep their dam because they like the pool or “waterfall” it creates. “We can show them the benefits of removal and let them know that if it’s a high priority, we could probably get grant funding to remove it,” Thompson said. “But we can’t force them to take it out.”
There are other headwinds. The proliferation of data centers — and their energy demands — have some people wondering whether old dams should be repurposed to generate electricity.
Building support
Perhaps no state illustrates the opportunities for accelerating dam removal better than Pennsylvania: It routinely leads the nation.
Last year, it took out 14 of the 100 dams removed nationwide. In 2024, it removed 27 — a quarter of all removals. (Not all were in the Bay watershed.)
“We have more dam owners that are interested in removal than we can feasibly get to,” said David Dippold, fish passage biologist with the Pennsylvania Fish and Boat Commission.
He said the state benefits from a longstanding “culture of connectivity” between state agencies, nongovernmental organizations, county conservation districts and others who promote dam removals. That means more people identifying dams and talking to owners.
They also promote benefits beyond helping migratory fish, which are often unlikely to show up because of downstream blockages. Even non-migratory species like brook trout benefit, as they gain access to more food sources and areas that provide buffers from extreme temperatures. Studies show fish diversity often increases as dams are removed.
The state also has a streamlined permitting system, envied by many others, in which dam removals are treated differently than bridges or other developments that impact floodplains.
The permitting system, Dippold said, recognizes that removals help “fix” a waterway, whereas doing nothing has its own impact: more maintenance, water quality degradation and impacts to fish. “There’s a cost to inaction,” he said.
The state doesn’t have a designated funding source, but projects often secure money from its Growing Greener program.
American Rivers’ plan to accelerate removals in part mimics Pennsylvania’s approach by creating “communities of practice” in each state. Those will bring together state, local and federal government officials, as well as scientists and nonprofit organizations, to identify dams for potential removal.
One of the goals is to create a pool of potential projects and, when possible, conduct preliminary work so removals can start sooner when opportunities arise.
The effort will include outreach to dam owners, highlighting the costs of maintaining structures and the liability issues if something goes wrong.
There have been 1,243 recorded dam failures or emergency interventions in the country, according to American Rivers, 80% of which were in the last 20 years.
“These things are 100 years old,” Schellhammer said. “It’s not a matter of ‘if’ it’s going to go. It’s ‘when.’”
The approach also aims to appeal to broader audiences. While the initial wave of removals focused on fish passage, new efforts recognize that many people have other motivations. They may want to remove a safety hazard, avoid a portage on a water trail or improve the looks of a waterway.
The Bloede Dam near Baltimore, for instance, helped migratory river herring and eels, but a major reason for the project was that nine people had drowned there since the 1980s. Dock Street Dam on the Susquehanna River in Harrisburg, now eyed for possible removal, is even deadlier. In the last century, 29 people have perished.
Or people may want to improve their communities. Last year, two dams across the Juniata River in Bedford, PA, were removed in large part because a member of the town council wanted to revitalize the riverfront. The project included shoreline enhancements, tree plantings and other amenities.
Whatever the reason, making the region’s — and the nation’s — rivers run mostly free is a daunting task. “We’re in it for the long haul,” said Jessie Thomas-Blate, American Rivers Mid-Atlantic director of restoration. “The reality is [that] there are just tons of dams out there not being used for the purpose they were built for. No one knows why many were built in the first place.”