The zebra mussel (Dreissena polymorpha) is a small freshwater mussel. This species was originally native to the lakes of southern Russia, being first described in 1769 by the German zoologist Peter Simon Pallas in the Ural, Volga, and Dnieper rivers. These mussels are still found nearby, as Pontic (Black Sea) and Caspian species. However, the zebra mussel has been accidentally introduced to numerous other areas, and has become an invasive species in many different countries worldwide. They were invasive to the Great Lakes but in the 1990s, they invaded the Hudson River. They are commonly found on the bottom of ships and eat the algae that is food for fish. Without food, fish starve. Inspectors check ships for the mussels before they leave port. Scientists are trying to control the mussels.