Nine Eagles Lake IA 05-GRA-1361

Assessment Comments

Basis for Assessment

SUMMARY:  Assessed support of the Class A (primary contact recreation) uses as "partially supported."  The Class B(LW) aquatic life uses remained assessed as "partially supporting."  Fish consumption uses remain "not assessed."  EXPLANATION:  Levels of indicator bacteria at Nine Eagles 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 34 samples collected at Nine Eagles beach showed that levels of indicator bacteria (fecal coliforms) were generally low, with the overall geometric mean (40 orgs/100 ml) well below the state WQ 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 had geometric means (N = from 6 to 10 samples per period) greater than 200 orgs/100ml.; the maximum 30-day geometric mean was 151 orgs/100ml.   The maximum level of fecal coliforms in the 34 samples was 3,600 orgs/100 ml on June 22, 1999; this was one of two samples that exceeded the EPA-recommended single sample maximum density for fecal coliform bacteria of 400 orgs/100ml (the sample collected on July 27, 1999, contained 470 orgs/100 ml).   Two of the eight 30-day periods that contained one or the other of these samples had more than 10% of samples with greater than 400 orgs/100 ml.   During the 30-day period from June 1 to June 30, 12.5% of the samples (one sample) exceeded the 400 orgs/100 ml criterion.   During the 30-day period from June 7 to July 7, 11% of the samples (one sample) exceeded this criterion.   Thus, due to the occurrence of a 30-day period with more than 10% of samples exceeding 400 orgs/100 ml, the Class A (primary contact recreation) uses were assessed as "partially supported."  The high levels of indicator bacteria in the two samples at Nine Eagles beach are likely related to the elevated levels of indicator bacteria that occur during and after rainfall runoff events.   The Class B(LW) aquatic life uses remain assessed as "partially supporting" based on review and approval of the previous (1998) assessment (see above) by the DNR Fisheries Bureau in 2000.   Fish consumption uses remained "not assessed" due to the lack of fish tissue monitoring at this lake.