Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008, (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997 and 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to exceedances of the Class A1 indicator bacteria standard. Algae blooms that violate Iowa's narrative criteria protecting against aesthetically objectionable conditions also cause an impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported.” Fish consumption uses are assessed (evaluated) as “fully supported.” Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2006, 2007, and 2008 (2) results of the statewide survey of Iowa lakes conducted from 2006 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 1997 and 2006.
Note: Fish populations were renovated in fall 2003 due to an increasingly large population of yellow bass at this lake.
EXPLANATION: Results of IDNR beach monitoring at Lake Anita from 2006 through 2008 suggest that the Class A1 uses should be assessed (monitored) as “not supported.” Levels of indicator bacteria were monitored once per week during the primary contact recreation season (May through September)of 2006 (15 samples), 2007 (17 samples), and 2008 (25 samples) as part of the IDNR beach monitoring program. According to IDNR’s assessment methodology, all thirty-day geometric means for the three-year assessment period must be less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses. If a 5-sample, 30-day geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported”. This assessment approach is based on U.S. EPA guidelines (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
At Lake Anita beach, the geometric means of 6 thirty-day periods during the summer recreation season of 2007 were greater than the Iowa water quality standard of 126 E. coli orgs/100 ml. None of the geometric means exceeded the standard in 2006 and 2008. One of 15 samples exceeded the single-sample maximum in 2006 (7%), 6 of 13 (35%) samples exceeded the single-sample maximum in 2007 and one of 25 samples exceeded the single-sample maximum in 2008 (4%). The exceedences of the geometric mean standard suggest that the Class A1 uses be assessed as "not supported."
Results from the ISU and UHL lake surveys suggest that the Class A1 uses at Lake Anita are (monitored) as “partially supported” due to the occurrence of aesthetically objectionable conditions caused by nuisance algae blooms. Using the median values from these surveys from 2006 through 2008 (approximately 11 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 59, 67, and 65 respectively for Lake Anita. According to Carlson (1977) the chlorophyll a and total phosphorus values place Lake Anita in between the eutrophic and hypereutrophic categories. The Secchi depth value places Lake Anita in the eutrophic category. These values suggest high levels of chlorophyll a and suspended algae in the water, relatively good water transparency, and moderately high levels of phosphorus in the water column.
The level of inorganic suspended solids was relatively low at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Anita was 2.0 mg/L, which was the 25th highest of the 132 monitored lakes.
Data from the 2006-2008 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Lake Anita, which contributes to occasional nuisance algae blooms and the impairment at this lake. These data show that cyanobacteria comprised 68% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (28.5 mg/L) was the 36th highest of the 132 lakes sampled.
NOTE: Lake Anita was not monitored in 2004 and 2005 because of low water levels due to a lake draw down for restoration. Fish populations were renovated in fall 2003 due to an increasingly large population of yellow bass at this lake.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that the fishery at this lake has improved since the renovation in 2003. The ISU and UHL lake survey results show good chemical water quality at Lake Anita. During 2006 and 2008 there were no violations of the Class B(LW) criterion for ammonia (11 samples) or pH (11 samples). There was one violation of the Class B(LW) criterion for dissolved oxygen. Based on IDNR's assessment methodology this violation is not significantly greater than 10% of the samples and therefore does not suggest an impairment of the Class B(LW) uses.
Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake Anita in 1997 and 2006. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The fish contaminant data generated from the 1997 RAFT sampling conducted at Lake Anita show that levels of all contaminants from this monitoring were below advisory trigger levels. Follow up sampling conducted in 2006 showed that the composite samples of fillets from largemouth bass had levels of mercury below the advisory trigger level of 0.3 ppm. The level of mercury in the composite sample of largemouth bass fillets was 0.252 ppm. According to IDNR's assessment methodology these results suggest "full support" of the fish consumption uses at Lake Anita.
