In 2004, 19 northern snakeheads were captured in the Potomac River, and they were later confirmed to have become established (i.e., they were breeding). They are somewhat limited to that stretch of the river and its local tributaries, upstream by the Great Falls, and downstream by the salinity of Chesapeake Bay. Tests found they are not related to northern snakeheads found in other waters in the region, alleviating some concern of their overland migration. Northern snakeheads continue to be caught in the river as of 2012.