Assessment Comments
Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program, (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 the 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 (monitored) as “fully supported.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2002 through 2006 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted from 2005 through 2006 by University Hygienic Laboratory (UHL), (3) information from the IDNR Fisheries Bureau, (4) results from the IDNR-county voluntary beach monitoring program, (5) results of a fish kill investigation on June 9, 2007, and (6) results of U.S. EPA/IDNR fish contaminant monitoring in 2005.
EXPLANATION: Results of IDNR county beach monitoring from 2004 through 2006 suggest that the Class A1 uses are assessed (monitored) as "fully supported." Levels of indicator bacteria at Lost Island Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (15 samples), 2005 (15 samples), and 2006 (16 samples) as part of the IDNR county 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 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).
At Lost Island Lake beach, the geometric means of all 29 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. The percentage of samples exceeding Iowa’s single-sample maximum criterion (235 E. coli orgs/100 ml) was also less than 10% in all of the recreation seasons: 2004: 7%, 2005: 0%, 2006: 6%. According to IDNR’s assessment methodology and U.S. EPA guidelines, these results suggest full support of the Class A1 (primary contact recreation) uses.
For the 2008 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 and nuisance aquatic life. Data from the ISU and UHL lake surveys, show poor water quality at Lost Island 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 73, 63, and 67 respectively for Lost Island Lake. According to Carlson (1977) the Secchi depth value places Lost Island Lake in the hypereutrophic category, while the chlorophyll a and total phosphorus scores 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, very 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 8.5 mg/L, which was the 30th highest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at Lost Island Lake, which contributes to impairment at this lake. These data show that cyanobacteria comprised 83% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (43.5 mg/L) was also the 27th 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 from 2002-2006. 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 the IDNR 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 (2004-2007) 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 2002 through 2006 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 17 samples, and no violations of the Class B(LW) criterion for dissolved oxygen in 23 samples. The pH data show 3 violations of the Class A1,B(LW) criterion for pH in 23 samples (13%). 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 (monitored) 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. 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 RAFT sampling conducted at Lost Island 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.
