Illinois River (continued)

Figure 42: Illinois River Watershed Nitrate Concentrations (mg/L) (ISGS)

Figure 43: Illinois River Watershed Phosphorus Concentrations (mg/L) (ISGS)

In 1991, the ISWS publishes a report, “The Illinois River: Working for Our State,” that indicates an improvement in some aspects of water quality since 1972. Total suspended solids and harmful substances such as dissolved barium, manganese, and boron all decline in the upper Illinois and Des Plaines rivers between 1977 and 1989. Ammonia nitrogen, a product of some industrial processes and raw domestic wastes, also decline. Ammonia nitrogen is toxic to all aquatic life forms in part because it consumes oxygen, so declining levels represent improvement for aquatic life.

Before 1970, wastewater treatment plants were unable to eliminate ammonia nitrogen from the wastes. New technologies coupled with increased waste reduction result in dramatic reductions of ammonia nitrogen. Measures in Lockport in 1970 show values as high as 118,000 pounds per day. By 1982, these values are reduced to 40,000 pounds per day. In 1986-87 at Peoria, average concentrations are 11% of the 1971-72 levels. Overall, ISWS finds that water quality relative to organic pollution is better for the main stem of the Illinois River in 1986 than at any time since the I&M Canal opened.