In the summer of 1994, 6 years after they were first found in Lake St. Clair, zebra mussels were collected in the Arkansas, Cumberland, Hudson, Illinois, Mississippi, Ohio, Susquehanna, and Tennessee rivers. (Figure 3) shows December 1995 distributions in the United States and Canada. Within a relatively short time, this species has spread throughout the eastern United States and is spreading west. Zebra mussels have been transported westward in Louisiana via the Gulf Intercoastal Waterway and are now in the Atchafalaya Basin. They have also been found in Oklahoma on the Arkansas River. Lawrence (1995) discussed how these organisms have spread across the various river systems.