Between 1989 and 2011, 2,510 stream miles were opened to the migration of fish in the Chesapeake Bay watershed. In the Chesapeake Bay Watershed Agreement, the Chesapeake Bay Program adopted a goal to open an additional 1,000 miles to migratory fish from this 2011 "baseline." As of 2016, 1,126 additional miles have been opened, marking a 113 percent achievement of this goal. About half of these miles were opened in Virginia. Just under half were opened in Pennsylvania, and the remainder were opened in Maryland.
The removal of dams, culverts and other barriers from streams across the watershed allows shad, herring and other migratory fish to move between fresh- and saltwater habitats, which is critical if these fish are to reach their historical spawning grounds. In fact, the abundance of some of these species in the region depends on streams that are open to their movement.
Once one of the most valuable fisheries in the Bay, shad populations have declined in recent decades due to pollution, historic overfishing and the construction of dams. While shad abundance has increased from 11 percent of the Chesapeake Bay Program's goal in 2000 to 38 percent of this goal in 2016 , not all rivers have seen a consisent rise in the fish. Shad populations surpassed restoration goals in the Potomac River—thanks to improvements in water quality, a resurgence in underwater grass beds, moratoriums on shad harvest, an increase in habitat available to migratory fish, stocking efforts that reprint fish to rivers and kick-start local populations, and the overall suitability of the Potomac as shad habitat—but remain negligible in the upper James and Susquehanna and variable in the lower James, Rappahannock and York. Some variability is natural, but the continued scarcity of shad in the upper James and Susquehanna can be attributed to Bosher's and York Haven dams.