Clear Lake IA 02-WIN-841

Results of DNR beach monitoring from 2014 through 2016 suggest that the Class A1 uses are "Partially Supported." Levels of indicator bacteria were measured at multiple beaches located at Clear Lake as part of the DNR beach monitoring program. Clear Lake State Park Beach was monitored once per week during the primary contact recreation seasons(May through September) of 2014 (15 samples), 2015 (16 samples) and 2016 (17 samples), as part of the DNR beach monitoring program.McIntosh Beach were monitored once per week during the primary contact recreation seasons(May through September) of 2014 (17 samples), 2015 (20 samples) and 2016 (19 samples), as part of the DNR beach monitoring program. According to DNR’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 1000 orgs/100 ml during the three-year assessment period, the Class A1 uses should be assessed as “not supported.” Also, if a sampling season geometric mean exceeds the state criterion of 126 orgs/100 ml during the three-year assessment period and/or 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 State Park Beach, the geometric means from 2014, 2015 and 2016 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 34 E. coli orgs/100 ml in 2014, 49 E. coli orgs/100 ml in 2015 and 55 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 7% in 2014, 13% in 2015 and 18% in 2016. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "Fully Supported" of the Class A1 uses.

At McIntosh Beach, the geometric means from 2014 and 2015 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean from 2016, however, was greater than the Iowa water quality standard of 126 E. coli orgs/100ml and therefore suggests impairment of the Class A1 uses. The geometric mean was 101 E. coli orgs/100 ml in 2014, 118 E. coli orgs/100 ml in 2015 and 486 E. coli orgs/100 ml in 2016. The percentage of samples exceeding Iowa's single-sample maximum criterion (235 E. coli orgs/100 ml) was 29% in 2014, 35% in 2015 and 58% in 2016. The number of samples exceeding the single-sample maximum criterion was significantly greater than 10% in 2014, 2015 and 2016. According to DNR's assessment methodology and U.S. EPA guidelines, these results suggest "partially supported" of the Class A1 uses.

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Clear Lake are assessed (monitored) as "partially supported" due to poor water transparency based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 65, 60, and 59 respectively for Clear Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Clear Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and relatively low levels of phosphorus in the water column. The data show no violations of the Class A1 criterion for pH in 15 samples.

Note:ATMDL for turbidity and algae at Clear Lake was prepared by DNR and approved by EPA in 2005. Becausethe 2006, 2008, 2010, 2012, 2014 and 2016Section 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 2016 Integrated Report.

The level of inorganic suspended solids was moderately high at Clear Lake, and does suggest that non-algal turbidity may contribute to the impairment at this lake. The median level of inorganic suspended solids in Clear Lake (3.8 mg/L) was ranked 82nd among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a large population of cyanobacteria exists at Clear Lake, which suggests the potential for an impairment due to nuisance aquatic life These data show that cyanobacteria comprised 96% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (202.6 mg/L) was ranked 135th of the 138 lakes sampled. This median is in the worst 25% of the 138 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 from 2012-2016. 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. 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 remain assessed (evaluated) as “partially supported” due to cyanobacteria blooms.Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and no violations of the criterion for pH in 15 samples(0%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Clear Lake.

The Class C (drinking water) uses are not assessed due to the lack of recent information upon which to base an assessment. The only parameter collected as part of the ISU lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU surveys from 2012-2016 show that nitrate levels are extremely low at this lake (maximum value = 0.2 mg/l; median = 0 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C 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/DNR 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.