Attempts at large river restoration are few and largely experimental. We studied a newly constructed river-wetland project on the upper Mississippi River three years after its completion. Species inventories for fish began to be compiled in the spring of 1993. Coincidentally, record rainfall throughout the midwest resulted in extreme floods and caused flooding of the study area during 1993. Fish communities responded to flooding with increased species diversity immediately following the flood. Wetland habitats yielded eight species of fish prior to flooding in June of 1993 compared to 26 species collected at the same sites in August 1993 following the flood crest. June 1994 sampling caught 33 species, but they declined to 16 in subsequent collections during August 1994. Flooding served to provide at least a temporary increase in diversity.