Lake Manawa IA 06-WEM-1711

Assessment Comments

Monitored in 1990 and 1992 by ISU as part of the Clean Lakes Classification study (1994); monitored in 1996 for fish tissue (RAFT sampling); and monitored in 1999 for beach/bacteria sampling.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "fully supporting."  The Class B(LW) aquatic life uses remained assessed as fully supported / threatened"; fish consumption remained assessed as "fully supported."  EXPLANATION:  Levels of indicator bacteria at Lake Manawa 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 33 samples collected at this beach showed that levels of indicator bacteria (fecal coliforms) generally low, with the overall geometric mean (19 orgs/100 ml) well below the state WQ criterion of 200 orgs/100 ml.   The maximum level of fecal coliforms in the 33 samples was 200 orgs/100 ml on July 12, 1999; thus, no samples exceeded the state 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 200 orgs/100ml.; the maximum 30-day geometric mean was 39 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 supported / threatened" based on review and approval of the previous (1998) assessments by the DNR Fisheries Bureau in 2000.   Fish consumption uses remained assessed as fully supported (=FS) based on results of EPA/DNR fish tissue (RAFT) monitoring in 1996 that showed levels of all contaminants < ½ of respective FDA action levels and DNR levels of concern.