Assessment Comments
Assessment is based on: (1) results of the IDNR-UHL beach monitoring program in the summers of 2006, 2007, and 2008 (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2005 and 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) IDNR/EPA fish tissue (RAFT) monitoring in 1998, 2006, and 2008.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed Iowa’s water quality standard. Algal and non-algal turbidity also contribute to the impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported." Fish consumption uses are assessed (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the IDNR-UHL beach monitoring program in the summers of 2006, 2007, and 2008 (2) results of the statewide survey of Iowa lakes conducted from 2004 through 2007 by Iowa State University (ISU), (3) results of the statewide ambient lake monitoring program conducted in 2005 and 2008 by University Hygienic Laboratory (UHL), (4) information from the IDNR Fisheries Bureau, and (5) IDNR/EPA fish tissue (RAFT) monitoring in 1998, 2006, and 2008.
Note: A TMDL for impacts of siltation and nutrients at Lake of Three Fires was prepared by IDNR and approved by EPA in 2002; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Not all Section 303(d) impairments identified for the 2010 assessment/listing cycle (indicator bacteria), however, are addressed in the TMDL. Thus, this waterbody remains in Category 5a (impaired; TMDL required) for the 2010 assessment/listing cycle.
EXPLANATION: Results of IDNR-UHL beach monitoring from 2006 through 2008 suggest that the Class A1 uses are "not supported." Levels of indicator bacteria at Lake of Three Fires beach were monitored once per week during the primary contact recreation seasons (May through September) of 2006 (27 samples), 2007 (18 samples), and 2008 (24 samples) as part of the IDNR-UHL 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 of Three Fires beach, the geometric means of 17 thirty-day periods during the summer recreation seasons of 2006, 2007 and 2008 exceeded the Iowa water quality standard of 126 E. coli orgs/100 ml: 5 of 23 geometric means violated in 2006, 6 of 14 geometric means violated in 2007, and 6 of 20 geometric means violated in 2008. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 11% in 2006, 22% in 2007 and 13% in 2008. According to IDNR’s assessment methodology and U.S. EPA guidelines, the exceedences of the geometric mean criterion suggest impairment (nonsupport) of the Class A1 (primary contact recreation) uses.
Lake of Three Fires was sampled as part of IDNR’s Safe Lakes Program, which aims to identify sources of bacteria to selected beaches where bacteria levels have consistently violated the state water quality criteria. The Safe Lakes Program found that wildlife (mainly geese) were the likely source of bacteria to Lake of Three Fires. Geese were noted regularly during sampling. Also, bacteria levels throughout the watershed were found to be consistently low, while bacteria levels in the sand were very high suggesting that inputs from the watershed were less significant than bacteria inputs at the beach.
Results from the ISU lake survey and the UHL ambient lake monitoring program from 2004 through 2008 suggest that the Class A1 (primary contact recreation) uses for Lake of Three Fires be assessed (monitored) as “fully supported.” Using the median values from these surveys from 2004 through 2008 (approximately 17 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 55, and 68 respectively for Lake of Three Fires. According to Carlson (1977) the Secchi depth and total phosphorus values place Lake of Three Fires in between the eutrophic and the hypereutrophic categories while the chlorophyll a value places Lake of Three Fires in the eutrophic category. The 2010 values suggest relatively low levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and high levels of phosphorus in the water column. While these values show improvement over the 2006 assessment/listing cycle (Secchi depth TSI 69, chlorophyll a TSI 64, total phosphorus TSI 73) and the 2008 assessment/listing cycle (Secchi depth TSI 64, chlorophyll a TSI 63, total phosphorus TSI 68) IDNR's assessment methodology states that the TSI values for chlorophyll a and Secchi depth must be 63 or below for two consecutive assessment/listing cycles prior to being suggested for de-listing. Therefore the impairments for algae and turbidity remain for the 2010 assessment/listing cycle.
Based on data from the ISU and UHL surveys in 2004 through 2008, the median concentration of inorganic suspended solids was 2.5 mg/L, which was the 38th lowest concentration of the 132 lakes monitored by these programs. These levels show an improvement from the 2008 assessment/listing cycle (6.0 mg/L).
Data from the 2004-2008 ISU and UHL surveys suggest a relatively small population of cyanobacteria exists at Lake of Three Fires, which shows improvement over results of the 2008 assessment/listing cycle. These data show that cyanobacteria comprised 79% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (5.9 mg/L) was the 30th lowest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported” based on information from the IDNR Fisheries Bureau and results of the ISU and UHL lake surveys. Information from the IDNR Fisheries Bureau suggests that water clarity and fish populations have improved at Lake of Three Fires following a dredging project and fishery renovation initiated in 2004. However, high levels of algae and limited rooted aquatic plant growth remain concerns at this lake.
Results of the ISU and UHL lake surveys data from 2004-2008 also suggest "full support" of the Class B(LW) uses. These data show no violations of the Class B(LW) criteria for ammonia in 16 samples and only one violation of the Class A1,B(LW) criterion for pH in 17 samples (6%). The data show 2 violations of the criterion for dissolved oxygen in 17 samples (12%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples necessary to suggest impairment of the Class B(LW) uses.
The Class C (drinking water) uses remain "not assessed" due to lack of information upon which to base an assessment. The only parameter collected as part of the ISU and UHL lake surveys relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU and UHL surveys from 2004-08 show that nitrate levels are very low at this lake (maximum value = 3.0 mg/l; median = 0.1 mg/l in 17 samples) compared to the MCL for nitrate (10 mg/L), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Lake of Three Fires in 1998 and 2006. Although the composite samples of fillets from channel catfish contained low levels of most contaminants in both the 1998 and 2006 samplings, the samples of largemouth bass had elevated levels of mercury. Levels of mercury in the composite sample of largemouth bass fillets were 0.235 ppm in the 1998 sample and 0.37 ppm in the 2006 sample. The level of mercury in the 2006 sample exceeds the IDNR/IDPH trigger level of 0.3 ppm for a one meal/week advisory. 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. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. But, this elevated level does indicate a concern and the need to conduct additional monitoring to better define contaminant levels in fish from this lake. Follow up monitoring was conducted in 2008. The level of mercury in the composite sample of largemouth bass fillets was 0.207 ppm, which is below the one meal per week advisory trigger level (0.3 ppm). Therefore the fish consumption uses at Lake of Three Fires will remain assessed as "fully supported."
