These fish were once killed as a nuisance by catch because they damaged fishing gear. When their meat and eggs became prized, commercial fishermen targeted them. Between 1879 and 1900, the Great Lakes commercial sturgeon fishery brought in an average of 4 million pounds (1800 metric tons) per year. Such unsustainable catch rates were coupled with environmental challenges such as pollution and the construction of dams and other flood control measures. Sturgeon, which return each spring to spawn in the streams and rivers in which they were born, found tributaries blocked and spawning shoals destroyed by silt from agriculture and lumbering. In the 20th century, drastic drops in sturgeon catches, increased regulations, and the closure of viable fisheries occurred. Currently, 19 of the 20 states within the fish's original U.S. range list it as either threatened or endangered.