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 tissue monitoring in 2002.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not 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 algae 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 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 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 and 2008 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 2008 Integrated Report.
EXPLANATION: Results of IDNR beach monitoring from 2004 through 2006 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Clear Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (22 samples), 2005 (23 samples), and 2006 (28 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) 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 A 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).
At Clear Lake beach, the geometric means of 30 thirty-day periods during the summer recreation seasons of 2004, 2005 and 2006 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 11 of 18 geometric means violated in 2004, 12 of 19 geometric means violated in 2005, and 7 of 24 geometric means violated in 2006. Also, the percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was significantly greater than 10% in the following recreation seasons: 2004: 45%, 2005: 48%, 2006: 21%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest impairment (nonsupport) of the Class A1 (primary contact recreation) 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 2004 through 2006, however, suggest that the Class A1 uses should be assessed (monitored) as “fully supported.” Levels of indicator bacteria were monitored once per week during the primary contact recreation seasons (May through September) of 2004 (16 samples), 2005 (17 samples), and 2006 (16 samples) as part of the IDNR beach monitoring program. At McIntosh Woods beach, the geometric means of all 37 thirty-day periods during the summer recreation seasons of 2004, 2005 and 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 beach. Also, the number of samples exceeding the one-time maximum criteria of 235 orgs/100 ml was below 10% for all years (2004: 0%, 2005: 6%, 2006: 6%). Thus, results from McIntosh Woods beach do not suggest an impairment of the Class A1 uses of Clear Lake.
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 2002 through 2006 (approximately 23 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 66, and 66 respectively for Clear Lake. According to Carlson (1977) the Secchi depth places Clear Lake in the hypereutrophic category, while the values for chlorophyll a and total phosphorus place Clear Lake between the eutrophic and hypereutrophic categories. These values suggest high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and high levels of phosphorus in the water column.
The levels of inorganic suspended solids were very high at this lake and suggest that non-algal turbidity contributes to poor water transparency and the impairment at Clear Lake. The median level of inorganic suspended solids in Clear Lake (9.0 mg/L) was the 27th highest concentration among the 132 lakes sampled by the ISU and UHL lake surveys.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Clear Lake, which contributes to impairment at this lake. These data show that cyanobacteria comprised 79% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (67.7 mg/L) was also the 17th highest of the 132 lakes sampled. This median is in the worst 25% of the 132 lakes sampled. The presence of a large population of cyanobacteria at this lake suggests a potential violation of Iowa’s narrative water quality standard protecting against the occurrence of nuisance aquatic life. This assessment is based strictly on the distribution of the lake-specific median cyanobacteria values for the 2002-2006 period. Median levels greater than the 75th percentile of this distribution were arbitrarily considered to represent potential impairment. No other criteria exist, however, upon which to base a more accurate identification of impairments due to cyanobacteria. The assessment category for assessments based on level of cyanobacteria will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence) to account for this lower level of confidence.
The Class B(LW) (aquatic life) uses are assessed as “fully supported” based on information from the IDNR Fisheries Bureau, results from the ISU and UHL lake surveys and physical/chemical monitoring associated with IDNR’s beach monitoring program. The ISU and UHL lake survey results show good chemical water quality at Clear Lake. During 2002-2006 there were no violations of the class B(LW) criterion for ammonia (16 samples), or dissolved oxygen (23 samples), and two violations in 23 samples of the pH criterion (9%). Based on IDNR’s assessment methodology, the two violations of the pH criterion are not significantly greater than 10% of the samples and therefore do not constitute an impairment of water quality at Clear Lake. The physical/chemical data associated with the beach monitoring program from 2004 through 2006 show no violations of the Class B(LW) criteria for dissolved oxygen (117 samples) and 9 violations of the pH criterion in 117 samples. According to IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest “full support” of the Class B(LW) uses of Clear Lake.
A dredging project is set to occur in the spring of 2008, which will likely reduce the internal resuspension of sediment and phosphorus in the lake. Additionally, a population of zebra mussels has developed in the lake. The consequences to the lakes water quality and algal population have not been seen as of 2007.
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 2002. The composite samples of fillets from channel catfish and walleye had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: <0.0181 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.045 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 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 2002 RAFT sampling conducted at 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.
