West Okoboji Lake - Main Basin South IA 06-LSR-1653

Assessment Comments

Monitored in 1990 by ISU as part of the Clean Lakes Classifcation study; in 1993 & 1995 for surveys of Water Supply Reservoirs (Miller & Kennedy 1993, 1995); and RAFT Monitoring in 1995.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "fully supporting."  The Class B(LW) aquatic life uses, the Class C (drinking water) uses, and the fish consumption uses remained assessed as "fully supporting."  EXPLANATION:  Levels of indicator bacteria at Gull Point beach were monitored approximately twice per week during summer 1999 by DNR Parks, Recreation and Preserves Division as part of a beach monitoring program at 11 state-owned lakes.   Results of the 35 samples collected at this beach showed that levels of indicator bacteria (fecal coliforms) were very low compared to other Iowa lakes, with the overall geometric mean (11 orgs/100 ml) well below the state water quality criterion of 200 orgs/100 ml.   The maximum level of fecal coliforms in the 34 samples was 30 orgs/100 ml on June 8, 1999; thus, no samples exceeded the Iowa water quality criterion of 200 orgs/100 ml.   According to U.S.  EPA guidelines for determining "full support" of primary contact uses (U.S.  EPA 1997b, page 3-35), the geometric mean of fecal coliform bacteria levels should not exceed 200 orgs/100ml based on at least five samples in a 30-day period.   In addition, not more than 10% of the total samples taken during any 30-day period should have a density that exceeds 400 orgs/100 ml.   None of the sixteen 30-day periods during summer 1999 had geometric means (N = from 6 to 10 samples per period) greater than the state water quality criterion of 200 orgs/100ml.; the maximum 30-day geometric mean was 13 orgs/100ml.   No samples exceeded the EPA-recommended single sample maximum density for fecal coliform bacteria of 400 orgs/100ml.   Thus, the Class A (primary contact recreation) uses were assessed as "fully supported."  The Class B(LW) aquatic life uses remain assessed as "fully supporting" based on review and approval of the previous (1998) assessments by the DNR Fisheries Bureau in 2000.   The Class C drinking water use remained assessed as "fully supporting" based on (1) the assessment developed for the 1996 report (see above) and (2) the 1998 results of the Novartis "Iowa Voluntary Atrazine Monitoring Program."  This monitoring showed that the time-weighted mean level of atrazine in samples collected from the Milford raw water source from January to December 1998 (0.1 ug/l, N=31, maximum=0.5 ug/l) was well below the MCL of 3.0 ug/l.   Based on DNR's Section 305(b) assessment methodology, if average contaminant levels and maximum values are below the MCL, "full support" of drinking water uses is suggested.   Fish consumption uses remained assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring in 1995 that showed levels of all contaminants in the composite sample of fillets from carp and yellow perch were less than ½ of respective FDA action levels and DNR levels of concern (see assessment for the 1996 report).