A total of 112 fish species has been recorded in Will County over the past 107 years; six species are endangered or threatened in Illinois, and 11 species are nonnative. River and creek ecosystems are the predominant fish habitat within the county. Each watershed has its own individual story. For example, Exline Slough fishes represent what would have been found in regional prairie sloughs and wetlands prior to conversion of natural lands for agriculture. Some creeks, such as Plum Creek, hold an above-average diversity of fishes but are isolated by dams and environmental degradation. If the fishes in these creeks are eliminated, they would not return because of limited opportunities for recolonization. Riparian wetlands along the Des Plaines and Kankakee rivers serve as nurseries for juvenile fishes. Hickory Creek is one of the most studied creeks in the Midwest, but unfortunately loss in biodiversity is what has been documented. Jackson Creek is reminiscent of Hickory Creek historically. Hopefully it will not suffer the same fate. The greatest threat to Will County fishes is urban sprawl from the city of Chicago and its associated habitat degradation. Not only does physical alteration of habitat and water quality pose a threat to native biodiversity, but biological pressures from nonnative species introductions do as well. Populations of the Round Goby Apollonia melanostoma and Oriental Weatherfish Misgurnus anguillicaudatus are established and growing. The Silver Carp Hypophthalmichthys molitrix and Bighead Carp Hypophthalmichthys nobilis are anticipated to colonize the larger rivers sometime in the next few years. All is not bad news. Water quality in the Des Plaines River appears to be improving as evidenced by the recent collection of a Freckled Madtom Noturus nocturnus for the first time in over 100 years. Large populations of environmentally sensitive redhorses (Moxostoma spp.) live in the Kankakee River, as does the endangered Pallid Shiner Hybopsis amnis. A variety of quality aquatic habitats in Will County deserve management and protection.