Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2004, 2005, and 2006 (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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 (evaluated) as “partially supported” due to aesthetically objectionable conditions caused by algae blooms. The Class B(LW) (aquatic life) uses are assessed (evaluated) 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 2004, 2005, and 2006 (2) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 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 suggest that the Class A1 uses should be assessed (evaluated) as “fully supported.” Levels of indicator bacteria were monitored once per week during the primary contact recreation season (May through September) 2006 (15 samples) as part of the IDNR beach monitoring program. 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. Because only one year of data was collected due to this these data are considered not sufficient to accurately characterize current water quality conditions, therefore the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). According to IDNR’s assessment methodology, two conditions need to be met for results of beach monitoring to indicate “full support” of the Class A1 (primary contact recreation) uses: (1) all thirty-day geometric means for the three-year assessment period are less than the state’s geometric mean criterion of 126 E. coli orgs/100 ml and (2) not more than 10 % of the samples during any one recreation season exceeds the state’s single-sample maximum value of 235 E. coli orgs/100 ml. 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.” Also, if more than 10% of the samples in any one of the three recreation seasons exceed Iowa’s single-sample maximum value of 235 E. coli orgs/100 ml, the Class A1 uses should be assessed as “partially 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 all 11 thirty-day periods during the summer recreation season of 2006 were below the Iowa water quality standard of 126 E. coli orgs/100 ml. These results suggest generally low levels of indicator bacteria at this lake. Also, less than 10% of the samples in 2006 (7%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. Thus, these results do not suggest an impairment of the Class A1 uses of Lake Anita.
Results from the ISU and UHL lake surveys, however, suggest that the Class A1 uses at Lake Anita are (evaluated) “partially supported” due to the occurrence of aesthetically objectionable conditions caused by nuisance algae blooms. Using the median values from these surveys from 2002 and 2006 (approximately 9 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 65, and 63 respectively for Lake Anita. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Lake Anita in between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column.
The level of inorganic suspended solids was moderately high at this lake and does not suggest impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lake Anita was 4.4 mg/L, which was the 60th highest of the 132 monitored lakes.
Data from the 2002-2006 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 99% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (22.0 mg/L) was the 57th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (evaluated) as “fully supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys, and results of physical/chemical monitoring associated with the IDNR-UHL beach monitoring program. 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 2002 and 2006 there were no violations of the class B(LW) criterion for ammonia (3 samples), dissolved oxygen (8 samples), or pH (8 samples). Based on IDNR’s assessment methodology these results do not suggest an impairment (full support/evaluated) to the Class B(LW) uses of Lake Anita. The physical/chemical monitoring results from the IDNR-UHL beach monitoring program showed one violation of the Class B(LW) criterion for dissolved oxygen in 15 samples (7%). Results of pH monitoring through the IDNR-UHL beach monitoring program also show 1 violation of the Class B(LW) criterion for pH in 15 samples (7%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not constitute an impairment of the Class B(LW) uses of Lake Anita.
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.
