By the Numbers: 33

Each spring, migratory fish use the rivers and streams of the Chesapeake Bay watershed to move between fresh water and the saltier ocean. Anadromous species—like American shad, hickory shad and blueback herring—return from the ocean to lay their eggs in fresh water, while catadromous species—like the American eel—move from streams to the ocean to spawn. While dams and culverts can block the movement of these fish, dam removal and fish passage construction projects have reopened thousands of area stream miles to fish migration.

According to the Maryland Department of Natural Resources, 33 fish species have ascended a fish lift, ladder or other structure in the state. While this indicates the value of fish ladders, lifts and other structures that help move fish over dams, it’s important to note the shift that new research has brought to fish passage restoration.

“Our [fish passage] program has changed over the years,” said Nancy Butowski, who manages fish passage in Maryland and serves as a member of the Chesapeake Bay Program’s Fish Passage Workgroup. “In the 1990s, it was focused on providing fish passage through ladders. But…fish passages are not 100 percent efficient. Now, we prefer dam removal.”

Dam removal can benefit a wider range of species—like the resident fish who also move up and downstream at different times of year—and the stream itself, Butowski said. Depending on the dam, its removal can even benefit human health: there have been several deaths at the Patapsco River’s Bloede Dam, which is slated for removal.

Maryland has worked with Pennsylvania, Virginia and the Nature Conservancy to develop a tool that will prioritize fish passage restoration projects. It takes close to 40 different characteristics into account, including how many miles a project would open, how much a project would cost and whether there are migratory fish currently using the waterway. Through the Chesapeake Bay Watershed Agreement, the Bay Program has committed to reopening 1,000 more stream miles to migratory fish by 2025. Learn more about our work to reopen fish passage.