Assessment Comments
Assessment is based on: (1) the results of the IDNR-UHL beach monitoring program in summers of 2010, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 2002.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to violations of the state water quality criteria for indicator bacteria. In addition, the ISU and UHL lake surveys suggest “partial support” of the Class A1 uses due to poor water transparency primarily due to high levels of inorganic suspended solids, and secondarily due to cyanobacteria blooms. The Class B(LW) (aquatic life) uses remain assessed (monitored) as “fully supported.” Fish consumption uses remain assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) the results of the IDNR-UHL beach monitoring program in summers of 2010-2012, (2) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) results of U.S. EPA/IDNR fish tissue monitoring in 2002.
Note: A TMDL for nutrients and algae at Clear Lake was prepared by IDNR and approved by EPA in 2005. Because the 2006, 2008, 2010, 2012 and 2014 Section 303(d) impairments due to indicator bacteria were not addressed in the TMDL, this waterbody will remain in Category 5a (impaired; TMDL required) of Iowa's 2014 Integrated Report.
EXPLANATION: Results of IDNR beach monitoring from 2010 through 2012 suggest that the Class A1 uses are “partially supported." Levels of indicator bacteria at Clear Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (21 samples), 2011 (32 samples), and 2012 (30 samples) as part of the IDNR beach monitoring program. 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) the geometric mean of the samples from each recreation season of 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 sampling season 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 significantly 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).
NOTE: Based on consultation with EPA Region 7 staff in 2011, IDNR’s methodology for assessing impairments based on the geometric mean water quality criterion was changed. Prior to the 2012 listing cycle, IDNR calculated geometric means for lakes based on a 30-day periods within the recreational season. Any violation of one of these 30-day periods within 3 years resulted in an impairment of the Class A1 uses of that lake. Because water quality standards do not identify a 30 day period but instead a recreational season, Region 7 concurred that the approach used for rivers and streams with less frequent bacteria data (seasonal geometric means) would be appropriate for identifying §303(d) impairments at lake beaches. Thus, for the 2012 listing cycle, IDNR identified primary contact recreation impairments for lakes when the geometric mean of all samples from the recreation season of a given year exceeded the geometric mean criterion. This does not impact the way IDNR assesses beaches for closure to protect the recreating public in the short term.
At Clear Lake beach, the geometric means from 2010, 2011, and 2012 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 113 E. coli orgs/100 ml in 2010, 27 E. coli orgs/100 ml in 2011, and 33 E. coli orgs/100 ml in 2012. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 6% in 2011, 13% in 2012 and 43% in 2010. The results from 2010 indicate that significantly greater than 10% of the samples exceeded the single-sample maximum criterion and therefore suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “partial support” of the Class A1 uses.
Clear Lake was monitored as part of IDNR’s Safe Lakes Program, which aims to identify sources of bacteria at selected beaches where bacteria levels have consistently violated the state water quality criteria. The Safe Lakes Program found that resuspension of bacteria throughout the lake along with geese, raccoons, and humans were the likely sources of bacteria to Clear Lake Beach.
Results of IDNR beach monitoring at McIntosh Woods Beach at Clear Lake from 2010 through 2012 suggest that the Class A1 uses should be assessed (monitored) as “partially supported.” Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2010 (17 samples), 2011 (16 samples), and 2012 (15 samples) as part of the IDNR beach monitoring program. At McIntosh Woods beach, the geometric means from 2010-2012 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 105 E. coli orgs/100 ml in 2010, 110 E. coli orgs/100 ml in 2011, and 14 E. coli orgs/100 ml in 2012. The number of samples exceeding the one-time maximum criteria of 235 orgs/100 ml was 35% in 2010, 31% in 2011 and 0% in 2012. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% of the samples in 2010 and 2011 and therefore suggests that the Class A1 uses should be assessed as "partially supported."
Results from the ISU and UHL lake surveys suggest “partial support” of the Class A1 uses of Clear Lake. Using the median values from these surveys from 2008-2012(approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 57, and 60 respectively for Clear Lake. According to Carlson (1977) the Secchi depth and total phosphorus values place Clear Lake between the eutrophic and hypereutrophic categories, and the index values for chlorophyll a place Clear Lake in the eutrophic category. These values suggest relatively low 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 levels of inorganic suspended solids were moderately high at this lake and suggest that non-algal turbidity may contribute to poor water transparency and the impairment at Clear Lake. The median level of inorganic suspended solids in Clear Lake (3.6 mg/L) and ranked 66th of the 134 lakes sampled by the ISU and UHL lake surveys.
Data from the 2008-2012 ISU and UHL surveys suggest a moderately large population of cyanobacteria exists at Clear Lake, which may contribute to impairments at this lake. These data show that cyanobacteria comprised 73% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (42.2 mg/L) and ranked 11th of the 134 lakes sampled by UHL and ISU.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau and results from the ISU and UHL lake surveys. The ISU and UHL lake survey results show good chemical water quality at Clear Lake. During 2008-2012 there were no violations of the class B(LW) criterion for ammonia (14 samples),dissolved oxygen (14 samples), and pH. Based on IDNR’s assessment methodology, these results suggest "full support" of the Class B(LW) uses.
A dredging project was completed in 2009, which will likely reduce the internal resuspension of sediment and phosphorus in the lake for future assessments. Additionally, a population of zebra mussels has developed in the lake. Sediment, phosphorus, and algae levels have all declined slightly since the 2010 assessment and listing cycle.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Clear Lake in 2012. The composite samples of fillets from walleye and channel catfish had low levels of contaminants. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.18 ppm. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: total PCBs: 0.04 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2012 RAFT sampling conducted at this Clear Lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.
