Assessment is based on results of IDNR ambient monthly monitoring near Janesville.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses were assessed as "fully supported." Fish consumption uses remain not assessed. The source of data for this assessment is the results of monthly monitoring from October 1999 through September 2001 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co. EXPLANATION: The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station near Janesville in 2000 and 2001. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 24 samples collected or for toxic metals and toxic organic compounds in the four samples analyzed during this biennial period. Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units. Two of the 24 samples had pH values greater than 9.0 units, with a maximum value of 9.1 units. Both violations occurred on days when dissolved oxygen levels were well above 100% saturation: April 12, 2000 (pH=9.1; % DO saturation=125%); May 4, 2000 (pH=9.1; DO saturation=140%). These conditions suggest that high levels of primary productivity resulted in the high levels of pH. Because these violations are more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment. Fish consumption uses were not assessed due to the lack of recent fish tissue monitoring in this river segment.