Assessment Comments
Assessment is based on results of monitoring conducted by Iowa State Univ. as part of the ACOE's Des Moines R./Saylorville Res./Red Rock Res. water quality study.
Basis for Assessment
SUMMARY: Continue to assess support of the Class A (primary contact recreation) uses as "fully supported." The Class B(WW) aquatic life uses are assessed as "fully supported," and the fish consumption uses are assessed as "fully supported / threatened." The assessments of support of the beneficial uses are based on results of water quality monitoring conducted by Iowa State University (under contract with the U.S. Army Corps of Engineers) during the 2000-2001 biennial period as part of the Des Moines River Water Quality Study (see Lutz et al. 2001 and Lutz and Esser 2002). EXPLANATION: The Class A (primary contact recreation) uses remain assessed as "fully supported." ISU/ACOE monitoring of levels of indicator bacteria (fecal coliforms) during summers of 2000 and 2001 at mid-lake near the dam and at three locations at each of the two swimming beaches (North Overlook and Whitebreast) showed that geometric mean levels of indicator bacteria were far below the state water quality criterion of 200 orgs/100 ml. Geometric means for the 2000-01 period were as follows: 4 orgs/ 100 ml at the mid-lake station (16 sampling events; max = 100 orgs/100 ml); 16 orgs/100 ml at North Overlook Beach (16 sampling events; max daily mean = 335 orgs/100 ml); 12 orgs/100 ml at Whitebreast Beach (16 sampling events; max daily mean = 207 orgs/100 ml). The Class B(WW) aquatic life uses were assessed as "fully supported:" none of the 32 samples collected from the mid-lake (surface) station during the biennial period exceeded Class B(WW) WQ criteria for conventional parameters (dissolved oxygen, pH, and ammonia) (samples were not analyzed for toxic metals). Fish contaminant monitoring conducted in Red Rock Reservoir by ISU/ACOE in 2000 and 2001 showed that levels of contaminants (chlordane, alachlor, trifluralin, and chlorpyrifos) in composite samples of whole fish common carp were all less than ½ of the respective FDA action levels or DNR levels of concern. The level of dieldrin in the sample of whole-fish carp collected in May, 2001, however, contained 0.172 ppm of dieldrin. This level is above one-half the FDA action level of 0.300 ppm. Thus, based on IDNR guidelines for Section 305(b) reporting, fish consumption uses are assessed as "fully supported / threatened." Levels of organochlorine contaminants such as dieldrin tend to be higher in whole-fish versus fillet samples. Thus, levels of dieldrin in fillets could be expected to be less than one-half the FDA action level. For more information on ISU/ACOE water quality monitoring at Red Rock Reservoir, see Lutz et al. (2001) and Lutz and Esser (2002).
