Lake Macbride IA 02-IOW-629

Assessment Comments

Assessment is based on (1) results of IDNR beach monitoring , (2) ISU lake survey , (3) ISU report on lake phytoplankton communities, and (4) surveys by IDNR Fisheries Bureau.

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 supporting / threatened"; fish consumption uses were considered "not assessed."  The level of this lake was lowered in 2000 for lake improvement work.   EXPLANATION:  Levels of indicator bacteria at Lake MacBride 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) 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 40 orgs/100 ml on July 26, 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 / threatened" based on review and approval of the previous (1998) assessments by the DNR Fisheries Bureau in 2000.   Fish consumption uses were previously assessed as fully supported (=FS) based on results of EPA/DNR fish tissue (RAFT) monitoring in 1991 that showed levels of all contaminants in the composite sample of fillets from channel catfish were less than ½ of respective FDA action levels and DNR levels of concern.   Results of this monitoring are now considered too old (greater than five years) to assess the current levels of contaminants in fish.   Thus, the assessment of fish consumption uses was changed from "fully supporting" to "not assessed."