A mill dam on Brandywine Creek in May 2019. Photo provided by Stroud Water Research Center
A mill dam on Brandywine Creek in May 2019. Photo provided by Stroud Water Research Center

The beneficiaries of removing mill dams in Delaware River watershed? ‘Fish, fish, fish’

| February 19, 2024

On a spring day more than 300 years ago, the people of the Lenape tribe gathered in their homeland along the Brandywine Creek in Delaware. 

Hundreds of fish had just begun to make their way from the Atlantic Ocean, up the Delaware River and into the Brandywine to spawn in the creek’s upstream headwaters in Pennsylvania. 

After a long, lean winter for the Lenape, these fish — now known as the American Shad — were greeted as relatives and the first source of fresh food for the Lenapes every year. But when Samuel Kirk built a dam in 1720 near where the Brandywine Creek meets the Christina River — which bridges the Brandywine with the Delaware River in the city of Wilmington — the shad could no longer swim to their ancestral spawning grounds upstream.

The Lenape, in turn, largely lost the springtime food source they’d relied on for thousands of years, according to Dennis Coker, the principal chief of the Lenape Indian Tribe of Delaware. And what wildlife remained in the area, Coker added, the Europeans hunted competitively, with a “voracious appetite.” 

“It’s very much akin to killing all of the buffalo for Plains Indians,” Coker said, “with the intention of starving them.” 

The Lenape asked the settlers to remove the dam in the mid-1730s, according to Coker. Their “request fell on deaf ears,” he said. And after the Europeans brought the smallpox virus that wiped out around 90 percent of the indigenous population, Coker said the Lenape started to leave the Brandywine.

While the Delaware River itself is not dammed, hundreds of mill dams were erected in its tributaries and beyond as Europeans closed in on more land and as the Industrial Revolution picked up in the mid-1700s. 

The dams were principally built to harness water power for the Europeans’ industrial mills — including several dams built for the old du Pont Powder Mill in Delaware, where the Hagley Museum and Library now sits, in the early 1800s. 

Over the years, European colonists built a total of 11 small dams within a 12-mile stretch along the Delaware portion of the Brandywine, with 20 more built along the Pennsylvania portion. 

In the last 30 years, long after the various mills fell out of use and into disrepair, environmental groups and researchers have intensified efforts to remove these dams to restore fish passage and reconnect communities long segmented or displaced, like the Lenape.

Assessing the damage

The total number of dams remaining across the Delaware River watershed is untold, according to Marc Peipoch, an ecosystem ecologist and researcher with the Stroud Water Research Center. 

The U.S. Army Corps of Engineers has catalogued at least 90,000 dams taller than 6 feet in the United States, but according to the nonprofit advocacy group American Rivers, many of the smaller mill dams — which are usually around 3 feet tall — can often “fall through the cracks” and go uncounted. 

Peipoch said there could be as many as 70,000 mill dams in the Northeast alone.

Peipoch and Melinda Daniels, a senior research scientist at the Stroud center, have spent years studying how mill dams affect water quality and sedimentation in rivers — research that’s especially of interest in the Delaware River watershed, where dammed tributaries lead to the Delaware River basin, the source of drinking water for more than 14 million people

Read more: Dam removal leads to rebirth of the Paulins Kill

The size of a dam dictates its impact on the environment, according to Daniels.

Mill dams pose fewer dangers and cause fewer environmental disruptions to rivers than, say, the Hoover Dam, but even a small mill dam slows a river’s flow. The dams transform a river into a lake-like environment, Daniels said, making rivers more vulnerable to sediment collection, harmful algal blooms, and higher water temperatures that could cause water deoxygenation. 

But because the milldams often don’t rise above the riverbanks, heavy rains easily flush out sediment buildup, according to Daniels. Peipoch added that the overall effect of mill dams on water quality is “a drop in a bucket.” 

“The dams don’t change a whole lot when they are in place, and they won’t change much when they’re removed in terms of nutrients,” Peipoch said. “These dams are too small to make a significant change in the nutrient loads, or the amount of nutrients that flow down most of these rivers in the Eastern United States.”

The main catalyst behind dam removal projects, Peipoch said, is “fish, fish, fish.” 

“Putting a dam in a river is similar to a clogged artery in a body,” said Jessie Thomas-Blate, the director of river restoration for American Rivers. “It’s like building a wall in a river — it stops all the natural processes from moving forward in the river … it impacts fish on a very fundamental level.”

Climate change has placed a higher priority on dam removal for fish, Thomas-Blate added, as waters warm and fish search for cooler temperatures upstream.

Risks to humans

Mill dams pose risks for humans, too. Mill dams don’t provide flood control, and Thomas-Blate said that intensifying storms put old mill dams at greater risk of breaching. 

The dams also create an artificial waterfall that poses drowning risks. The force of the waterfall dropping down into the river below creates a “roller” — a powerful current that’s hard to escape once someone is trapped in it. 

The Bloede Dam in Maryland was removed in 2019 following the ninth recorded drowning death there. And as the Brandywine-Christina watershed has seen its population boom in recent years, Daniels said the number of people recreating along the Brandywine has “skyrocketed” too, raising the stakes of dam removal there. 

American Rivers has set a goal of removing 30,000 dams by 2050. It has mapped more than 2,000 dams removed nationally since 1912, with 50 to 60 dams removed per year. 

Many of these dams are privately owned, according to Thomas-Blate, though some are owned by the corporation, state or federal agency that owns the land nearby. 

Peipoch said between six to a dozen mill dams are typically removed in the Delaware River watershed each year, including the Brandywine Dam near the Christina River — which was dismantled in 2019, nearly three centuries after the Lenapes’ original request. 

And in the spring of 2020, the shad returned to the lower portion of the Brandywine Creek for the first time since the early 1700s.

Marc Peipoch, an ecosystem ecologist with Stroud, holds a sediment core he’d filled with sediment from the Christina River in December 2019. He and Johanna Hripto, the graduate student researcher also pictured, were collecting riverbed sediment above and below the Christina River’s Cooch-Dayett milldam in 2019, before it was removed. Researchers used the cores to measure the soil’s denitrification rate to find out how, or if, removing old dams could affect water quality and sedimentation in long-dammed rivers.


In 2005, the Brandywine Conservancy released its treatise on dam removal along the Brandywine, which renewed calls for the dams’ removal and raised awareness of the importance of the shad. 

In 2017, that document galvanized Hunter Lott, a Brandywine River resident, into forming the Brandywine River Restoration Trust — originally known as Brandywine Shad 2020 — to gather local organizations like the Brandywine Conservancy, the University of Delaware and the Hagley Museum and Library to fundraise for dam removals in the Brandywine. 

Within two years, the first dam on the Brandywine in Delaware was removed.

Dismantling dams and restoring rivers takes time — sometimes decades. Each state has different permitting systems for dam removal, according to Thomas-Blate, and funding for the demolition — which can cost anywhere from $50,000 to $1 million, she said — often comes from a variety of places. 

Lott said recent efforts to remove the first dam in the Brandywine date back to the 1970s, when the city of Wilmington built “fish ladders” in two dams to help fish passage. That was largely ineffective, Lott said, because the dam farthest downstream still hadn’t been removed. 

Read more: Man-made lakes, loved by humans, can harm the environment

If the effort to flatten these dams were a bulldozer, it’d have hundreds of arms — national efforts from the U.S. Fish and Wildlife to restore fish passage; advocacy groups like the Nature Conservancy and American Rivers that are fundraising and advocating dam removal projects; scientists like those at the Stroud Center; and the river’s residents, who have propped up dam removal efforts from the start.

Thomas-Blate and Lott both said their organizations are also acknowledging how these dams represent the watershed’s history of colonialism. They said they are now intentionally including tribal councils like the Lenape in discussions about dam removal.

Coker said it’s “an honor” to have a seat at that table. 

He’s attended the ShadFest in Wilmington — a festival celebrating the dam’s removal and the return of the shad — and witnessed the return of the shad himself. He’s served as the council’s leader for 25 years, and after years of hearing stories passed down by the state supposing the disappearance of the Lenape, he said these dam removal projects along the Brandywine feel like his tribe’s history is being acknowledged and like his ancestors’ request is finally being heard.

Lott said another Brandywine dam is slated for demolition in Delaware this winter, one of many dams targeted for removal across the Delaware River watershed. 

Removal of the dams along Bushkill Creek in Easton kicked off this past summer, and the Upper and Lower E.M. Collins dams in New Jersey are set to be demolished by 2025.

Lauren Yates

Lauren Yates

Lauren Yates is a freelance reporter based in the Adirondack Park in New York. She started her journalism career in 2021 as a daily reporter for The Adirondack Daily Enterprise in Saranac Lake, N.Y., where she develop


  1. Michael Castagner on March 2, 2024 at 1:29 pm

    Have the dams on the Rancocas creek in Burlington county been considered?

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