Migratory fish won’t return to polluted waters even if there are no dams to block their way, Dr. Craig said. The Delaware River, she said, is an example where industrial waste caused such poor water quality in the 1950s and ’60s that shad and other species would not migrate north of Philadelphia. Now, improved water quality has allowed the fish to move much farther up the river bordering northern New Jersey.
But supporters fear that the improvements could be set back by the Trump administration’s recently finalized rollback of the Waters of the U.S. rule, which will remove federal protections for intermittent streams and some freshwater wetlands, making it easier for landowners to build on those areas.
Still, the Brandywine dam project is pressing ahead, with the goal of removing or modifying Dams 3, 4, 6 and 11 this year, depending on the availability of funding from federal, state and private sources. This year’s projects will require an estimated $680,000, of which $410,000 would pay for the removal of Dam 4, a 150-foot structure that spans the creek between a state park and the site of an 18th-century textile mill where condominiums are now under construction.
Later, construction of a bypass channel for Dam 2 — which must be preserved because it diverts water to a Wilmington treatment plant — is expected to cost $1.4 million.
Funding so far has included $241,000 from the federal government as a result of the Delaware River Basin Conservation Act of 2016, which helps local conservation projects, and a matching grant from the State of Delaware, which owns three of the dams. Dr. Kauffman is hoping for a similar amount from the same federal source under a new round of funding early this year.
But even before any more dams have been removed, he’s confident that this year’s fish run — enabled by last year’s removal of Dam 1 — will show that the fish are ready to return.
“They will literally hit their heads on Dam 2,” he said. “They will just keep swimming until they can’t swim any more.”