The threehorn wartyback has a rounded, small to medium-sized shell (to 3 inches) that varies in color from shades of yellow and green to brown. This species is easily recognized by a central row of 1-4 large knobs on each valve in alternate positions.
This rare species historically occurred in the Great Lakes drainages including Lake St. Clair, western Lake Erie, and the Grand, Thames, and Detroit rivers. The species has not been found since 1992 in Lake St. Clair and the Detroit River and may be extirpated there due largely to the impacts of Zebra and Quagga mussels. It was last recorded from the Canadian side of Lake Erie in 1997. Pollution (sediment loading, nutrient loading, contaminants and toxic substances) related to both urban and agricultural activities represents a high and continuing threat at the three remaining riverine locations.
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