Navigation Dams

In the 1930s, navigation dams are built at three locations on the upper part of the river and at Peoria and La Grange. The locks at the latter are 110 feet by 60 feet (Illinois State Planning Commission 1940). These dams temporarily increase dissolved oxygen as the water passes over and through the dams. The construction of these dams, in concert with the reduction of the diversion from Lake Michigan, leads to a decrease of average current velocity from 2.01-4.02 km/hour prior to 1908 to 0.97 km/hour in 1966. The pools behind these navigation dams are filling with oxygen-demanding sediment which “in places resembles sludge from secondary sewage treatment plants” (Sparks and Starrett 1975).