The zebra mussel became established in the Great Lakes following accidental introductions, presumably from ballast water released from ocean-going ships. It since has spread through the Mississippi River and many tributaries. Its prolific growth clogs water intake structures, causing hundreds of millions of dollars in control costs. It competes with and grows over native mussels. Its high rate of water filtration has cleared the water column in many water bodies, decreasing the availability of food organisms for larval fish.