Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010, (5) results of a fish kill investigation on June 9, 2007, and (6) results of U.S. EPA/IDNR fish contaminant monitoring in 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to aesthetically objectionable conditions caused by poor water transparency due primarily to high levels of non-algal turbidity. Nuisance algae (cyanobacteria) blooms also contribute to an evaluated impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to a fish kill that occurred in 2007. Siltation and nutrient loading also remain concerns at this lake. Fish consumption uses are assessed (evaluated) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2006 through 2010 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2006 through 2008 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program in 2008, 2009, and 2010, (5) results of a fish kill investigation on June 9, 2007, and (6) results of U.S. EPA/IDNR fish contaminant monitoring in 2005.
Note: A TMDL for turbidity at Lost Island Lake was prepared by IDNR and approved by EPA in 2009; thus this lake is placed in IR Category 4a (TMDL approved) for the 2012 assessment/listing cycle.
EXPLANATION: Results of IDNR city/county beach monitoring from 2008 through 2010 suggest that the Class A1 uses are “fully supported." Levels of indicator bacteria at Lost Island Lake beach were monitored once per week during the primary contact recreation seasons (May through September) of 2008 (14 samples), 2009 (13 samples), and 2010 (12 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 Lost Island Lake beach, the geometric means from 2008, 2009, and 2010 were all below the Iowa water quality standard of 126 E. coli orgs/100 ml. The geometric mean was 14 E. coli orgs/100 ml in 2008, 20 E. coli orgs/100 ml in 2009, and 11 E. coli orgs/100 ml in 2010. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was 0% in 2008, 0% in 2009 and 0% in 2010. None of these are significantly greater than 10% of the samples and therefore do not suggest impairment of the Class A1 uses. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest “full support” of the Class A1 uses.
For the 2012 assessment/listing cycle, results from the ISU and UHL lake surveys indicate that the Class A1 (primary contact recreation) uses of Lost Island Lake are assessed as “not supported” due to aesthetically objectionable conditions caused by poor water transparency. Nuisance aquatic life (cyanobacteria) also causes an impairment at this lake. Data from the ISU and UHL lake surveys, show poor water quality at Lost Island Lake. Using the median values from these surveys from 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 69, 63, and 67 respectively for Lost Island Lake. According to Carlson (1977) the chlorophyll a, Secchi depth, and total phosphorus values all place Lost Island Lake in between the eutrophic and the hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, poor water transparency, and high levels of phosphorus in the water column.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was very high at this lake and suggests impairment due to high non-algal turbidity. The median inorganic suspended solids concentration at Lost Island Lake was 8.0 mg/L, which was the 25th highest of the 134 monitored lakes.
Data from the 2006-2010 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lost Island Lake, which causes an impairment at this lake due to nuisance aquatic life. These data show that cyanobacteria comprised 91% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (54.1 mg/L) was also the 19th highest of the 134 lakes sampled. This median is in the worst 25% of the 134 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 2006-2010. 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 (evaluated) as “partially supported” due to a fish kill on June 9, 2007. The kill was identified as a natural fish kill of crappies due to post-spawning stress. According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2008-2011) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Results of the ISU and UHL lake surveys from 2006 through 2010 suggest good chemical water quality at Lost Island Lake. Data from these surveys show no violations of the Class B(LW) criterion for ammonia in 22 samples, and no violations of the Class B(LW) criterion for dissolved oxygen in 21 samples. The pH data show 3 violations of the Class A1,B(LW) criterion for pH in 22 samples (14%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses of Lost Island Lake.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring at Lost Island Lake in 2005. The composite samples of fillets from walleye and carp had low levels of contaminants. Levels of primary contaminants in the composite sample of walleye fillets were as follows: mercury: 0.0244 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of carp fillets were as follows: mercury: 0.031 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 2005 sampling conducted in this lake show that the levels of contaminants do not exceed any of the advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
