Thousands of low dams sit in rivers across the United States, and most of them no longer do the job they were built for. They stopped running mills or generating power decades ago. What they still do is slow rivers down, trap sediment, and create dangerous currents that can trap and drown swimmers, boaters, and paddlers. Removing them is one of the most effective river restoration tools available, and the results are well documented.
A low dam (also called a low-head dam) is a small, often unremarkable-looking structure that spans a river from bank to bank, usually just a few feet tall. Many were built in the 1800s and early 1900s to power mills, generate electricity, or supply water to industry. Once the water flows over the top, many of them are designed to plunge into a "hydraulic jump" — a recirculating current that can trap a person underwater indefinitely. Researchers at Brigham Young University, who maintain the leading national database of low-head dam incidents, have documented more than 1,000 drownings at these structures over the past several decades, roughly a third of them people trying to rescue someone else. Their inventory now tracks more than 13,000 low-head dams nationwide.
There are currently 37 dam-related hazard points across the watershed — on the Great Miami River, Mad River, Stillwater River, Buck Creek, Twin Creek, Beaver Creek, and Greenville Creek. Of those, 32 are low dams: current structures needed for water infratructure or industry plus old mill and water-supply structures, grade-control dams, and remnants of industrial uses that have mostly outlived their original purpose. Paddlers can find the full list, with river mile locations and portage notes, on MCD's interactive water trail map.
Dam removal advocates and engineers generally point to four categories of benefit:
Public safety. Low dams are sometimes called "drowning machines" because the danger is invisible from the surface. Removing the structure eliminates the hazard entirely rather than just posting a warning sign.
Water quality and habitat. Dams slow rivers into pools where sediment, nutrients, and heat build up, which can drive algae growth and reduce oxygen for fish. Once a dam comes out, a river's natural riffle-pool structure returns, oxygenating the water and restoring habitat for fish and aquatic insects.
Fish and wildlife passage. Even a low dam can block the upstream movement of fish and other aquatic species. Removal reconnects river miles that had been cut off, sometimes for a century or more.
Cost and liability. Old dams need ongoing inspection, maintenance, and eventual repair, and dam owners carry liability for injuries and deaths. In many cases, removal costs less than rehabilitation and ends the liability question for good.
A common concern about removing a low dam is that the river will look empty or "dry up" once the pooled water behind the structure is gone. That's not what happens. A dammed river is artificially widened and deepened by the pool behind the low dam. Once the dam is out, the river simply returns to the size it would naturally be for the amount of water actually flowing through it — narrower, with more visible gravel bars and riffles, but still a continuously flowing channel.
Geomorphologists who study this process describe a predictable sequence. The sediment that had been trapped behind the dam for decades is exposed, and the river cuts a new, narrower channel down through that sediment, carrying some of it downstream and leaving the rest as newly formed banks and floodplain alongside the active channel. A widely cited 2002 review of dam removal science in BioScience explains that this incision and channel narrowing typically produces a new equilibrium channel with its own floodplain as the river re-establishes a stable form suited to its natural flow and sediment supply. Studies of smaller dam removals in the Midwest, including one on Wisconsin's Baraboo River, found the newly exposed channel reached a stable form within months, especially after the first high-flow event moved the leftover sediment into place.
Vegetation follows the same pattern. Grasses and willows typically colonize the newly exposed sediment within one to two growing seasons, stabilizing the banks of the narrower channel. What looks like a "smaller river" right after a dam removal is really the river reappearing at its natural width — the wide, still pool was what was artificial in the first place.
The most direct evidence on this question in Ohio comes from a study MCD commissioned on the Great Miami River in downtown Dayton, near the Monument Avenue low dam. MCD hired University of Dayton biologist Jeff Kavanaugh, Ph.D., to sample fish and macroinvertebrates before the dam was modified for paddling (2014–2015) and again afterward (2017–2018). Macroinvertebrates — stream insects such as mayflies and caddisflies that spend part of their lives underwater — are used by scientists as an indicator of river health because many species are highly sensitive to low oxygen and poor water quality. The post-modification surveys found a diverse, abundant fish community and aquatic habitat quality that exceeded expectations for an urban river reach, according to MCD's water resources team.
Nationally, U.S. Fish and Wildlife Service and NOAA Fisheries data from the Elwha River in Washington State — site of the largest dam removal in U.S. history before the Klamath — shows a similar trajectory over a longer timeline. The Elwha and Glines Canyon dams, removed between 2011 and 2014, had blocked salmon and steelhead from more than 90% of the watershed for over a century. A decade after removal, Lower Elwha Klallam Tribe fisheries biologists reported coho salmon returns of around 6,000 adults in a single fall and Chinook salmon returns ranging from 2,000 to 7,000 adults, along with growing numbers of wild steelhead. NOAA Fisheries' monitoring program describes Chinook and steelhead populations as continuing to increase, though full recovery to historic abundance is expected to take decades. The tribe resumed treaty salmon fishing on the river in 2023 for the first time in more than a decade.
Ohio has several completed low dam removal projects that illustrate these benefits directly.
Tait Station Low Dam, Great Miami River, Dayton. Built in 1935 to supply cooling water to a coal-fired power plant, the dam outlived its purpose when the plant closed in 1983. The Miami Conservancy District acquired the dam in 1990 and removed it in 2018 in a $1.75 million project fully funded by the Ohio Department of Transportation as stream mitigation for road work elsewhere in the watershed. A 2015 U.S. Army Corps of Engineers study of the Great Miami River corridor had recommended the removal, and both the City of Dayton and Montgomery County passed resolutions supporting it. The project replaced the dam with a constructed rock riffle, which improved fish habitat and made the reach near Carillon Historical Park safer and more navigable for paddlers. The permitting agreement required five years of post-construction physical and biological monitoring of the restored river reach, running through 2023.
West Milton Low-Head Dam, Stillwater River. Built around 1910 to power a trolley line between Dayton and West Milton and later used for municipal water supply, this 100-year-old dam was removed in a matter of weeks in late 2014, coordinated by the Ohio River Foundation with support from Ohio DNR, Ohio EPA, the U.S. Fish and Wildlife Service, and the Army Corps of Engineers. The removal reconnected roughly 200 miles of the upper Stillwater River watershed to the river downstream and cost the Village of West Milton nothing. With this dam gone, the Stillwater is often cited as the longest free-flowing river in Ohio and carries a state Scenic River designation.
Englewood Lowhead Dam, Stillwater River. Five Rivers MetroParks removed this dam at Englewood Reserve in September 2009 in a $1.5 million project. It had been built for recreation but had become a safety hazard; removal restored the river's natural flow and improved both ecological condition and public safety.
Great Miami River, Piqua. The U.S. Fish and Wildlife Service is currently partnering on the Great Miami River Watershed Barrier Removal and Habitat Restoration project, which will remove three low-head dams and reconnect a 1.5-mile oxbow channel. USFWS expects the project to restore this segment of river to Exceptional Warmwater Habitat status — Ohio EPA's highest aquatic life use designation — while also protecting the City of Piqua's drinking water supply.
Great Miami River, Troy. The City of Troy's low dam removal project, developed from a USFWS-supported feasibility study, is expected to replace a single oxygenated pool below the dam with multiple oxygenated pools along the reach, which city officials say should increase spawning habitat for smallmouth bass and boost populations of forage fish like minnows and shiners.
Other Ohio low dam projects are underway or in planning, including a dam safing and whitewater park project on the Great Miami River in West Carrollton, and MCD's Hamilton Low Dam Removal Project, which recently secured a $2.45 million H2Ohio award toward its total estimated cost of about $7.66 million.
Ohio's projects are part of a much larger national trend. The most significant single dam removal project in U.S. history wrapped up in 2024 on the Klamath River in California and Oregon, where the Copco 1, Copco 2, Iron Gate, and John C. Boyle dams were all removed, reconnecting roughly 400 miles of river and opening the way for salmon runs that tribal nations in the region had been working toward for decades, according to American Rivers.
Nationally, the pace of dam removal has been accelerating. American Rivers, the conservation group that tracks removals since 1912, reported 100 dams removed across 30 states in 2025, reconnecting more than 4,893 miles of river — the most river miles reconnected in a single year on record. That brings the documented U.S. total to 2,350 dam removals since 1912, out of more than half a million dams nationwide. More than a quarter of the 2025 removals were low-head dams specifically. Pennsylvania has removed more dams than any other state, with 433 total since 1912, including 14 in 2025 alone. In 2024, Michigan, Minnesota, and Virginia also completed multiple removals, and the Forest Preserve District of Kane County, Illinois, began a nine-dam removal series on the Fox River.
The 5 larger dams on the Water Trail Map's hazard list — Germantown, Englewood, Lockington, Taylorsville, and Huffman — are a different category of structure entirely, and they aren't part of any removal conversation.
These are the Miami Conservancy District flood protection dams, built as part of a system that has protected the Miami Valley since 1922. Unlike low dams, they don't hold back water day to day. River flow simply passes through large concrete tunnels (conduits) built into each dam. The dams only hold back water during high-water events, when river levels rise too high to pass safely through. The rest of the time, there's no impoundment behind them — water moves through much as it would without the dam there.
These dams are inspected and maintained on an ongoing basis and remain a permanent part of the region's flood protection safey net.
A low dam that no longer serves its original purpose isn't a neutral piece of infrastructure sitting quietly in the river. It's an ongoing safety risk, a water quality problem, and a barrier to fish and wildlife, and it costs money to maintain whether anyone uses it or not. The record from Tait Station to West Milton to the Klamath shows what happens when that structure comes out: the water clears, fish move upstream again, and the drowning hazard is gone for good.
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