Fish Populations in Relation to Dissolved Oxygen in the Wisconsin River

Fish populations were sampled with an electroshocker, fyke nets, and small-mesh seine in a 309-km section of the upper Wisconsin River, where average summer dissolved oxygen concentrations at various sites ranged from less than 2 to more than 8 mg/liter. Percent sport fish, percent walleyes and yellow perch, percent Centrarchidae, number of fish species, and number of species of sport fish were all greater at sites where the average summer dissolved oxygen concentration exceeded 5 mg/liter than at sites where it was less. The results indicate that reduction of biological oxygen demand in waste effluents would benefit the sport fishery.