Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) This species is found throughout the Tennessee, Cumberland, and Ohio River basins, the upper Mississippi River, and the St. Lawrence River system from Lake Huron to Lake Ontario including their tributaries (Parmalee and Bogan, 1998). Due to much confusion surrounding the use of Unio nebulosus within the Villosa iris complex, Parmalee and Bogan (1998) chose to list all the described taxa from the Ohio, Tennessee, and Cumberland River systems as synonyms of Villosa iris and restrict the use of Villosa nebulosa to the species occurring in the headwaters of the Mobile Bay Basin. In Canada, it was historically known from the Ausable, Bayfield, Detroit, Grant, Maitland, Moira, Niagara, Salmon, Saugeen, Sydenham, Thames and Trent Rivers, as well as Lakes Huron, Ontario, Erie, and St. Clair; but it appears to have been lost from the lower Great Lakes and connecting channels, except for the Lake St. Clair Delta, but it is still extant in most rivers (COSEWIC, 2006). Recently this species has been confirmed to be likely extirpated from the main channel of the Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 2006).