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 Syngenta’s voluntary atrazine monitoring program (VMP) from 2004-2006, and (5) results of U.S. EPA/IDNR fish contaminant monitoring in 2005 and 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “fully supported/threatened.” The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to high turbidity and algae blooms that are adversely affecting the lake's fish populations. The Class C (drinking water) uses are assessed (monitored) as "partially supported" due to increased levels of turbidity. 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 Syngenta’s voluntary atrazine monitoring program (VMP) from 2004-2006, and (6) results of U.S. EPA/IDNR fish contaminant monitoring in 2005 and 2006.
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 Little River Lake beach were monitored approximately once per week during the primary contact recreation seasons (May through August) of 2004 (15 samples), 2005 (13 samples), and 2006 (14 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 Little River Lake beach, the geometric means of all 30 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: 8%, 2006: 7%. 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, however, indicate that the Class A1 (primary contact recreation) uses of Little River Lake are assessed as “fully supported/threatened” due to increasing levels of turbidity in the lake. Using the median values from these surveys from 2002 through 2006 (approximately 20 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 62, 61, and 60 respectively for Little River Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus scores all place Little River Lake in between the eutrophic and hypereutrophic categories. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column. Additional data from 2007 and 2008 indicates that Secchi depths have continued to decrease and suggest impairment for the 2010 assessment and listing cycle. Therefore, the lake is considered "fully supported/threatened" for this 2008 assessment.
Based on data from the ISU and UHL lake surveys, the level of inorganic suspended solids was high at this lake but does not suggest impairment due to non-algal turbidity. The median inorganic suspended solids concentration at Little River Lake was 5.3 mg/L, which was the 51st highest of the 132 monitored lakes.
Data from the 2002-2006 ISU and UHL surveys suggest a moderate population of cyanobacteria exists at Little River Lake. These data show that cyanobacteria comprised only 52% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (13.5 mg/L) was the 53rd lowest of the 132 lakes sampled. These results suggest full support of the Class A1 uses at Little River Lake.
The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” based on information from IDNR’s Fisheries Bureau. Information from the IDNR Fisheries Bureau indicates that Little River Lake experiences high turbidity and algae blooms. The water treatment plant at Little River Lake recorded the most turbid water clarity season during 2007 and the fishery is struggling to produce quality sportfish due to suppression of sportfish feeding and reproduction due to increased turbidity in the lake. Increasing turbidities in this lake are attributed to both the silt dam failure in 2007 adn due to loss of silt-storage capacity behind the silt dam. An increasing population of common carp also impact water quality in this lake.
Data from the ISU and UHL lake surveys from 2002 through 2006 show no violations of the Class B(LW) criterion for ammonia in 17 samples, one violation of the Class B(LW) criterion for dissolved oxygen in 20 samples (5%), and one violation of the Class A1,B(LW) criterion for pH in 18 samples (6%). Based on IDNR’s assessment methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest impairment of the Class B(LW) uses of Little River Lake.
The Class C (drinking water) uses are also assessed (monitored) as “partially supported” due to increasing turbidities in the lake following the failure of a silt dam at the upper end of the lake in 2007.
Results of Syngenta's "Iowa Voluntary Atrazine Monitoring Program" from 2004 through 2006, however, show low levels of atrazine in this lake and no impact to the Class C drinking water uses. This monitoring showed that the time-weighted mean levels of atrazine in the samples collected in calendar years 2004, 2005, and 2006 were well-below the MCL of 3.0 ug/l. The mean and median atrazine level over this three-year period (N=78) were 1.2 ug/L and 1.1 ug/L, respectively. The maximum value for this period was 2.7 ug/l. None of the 65 moving annual averages for atrazine for the years 2004, 2005, and 2006 at Little River Lake exceeded the MCL (maximum average = 1.6 ug/l). Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported." In addition, results of the ISU and UHL lake surveys from 2002-2006 show that nitrate levels are low at this lake (maximum: 7.1 mg/L, median: 0.2 mg/L) relative to the MCL (10 mg/L).
Fish consumption uses are assessed (monitored) as “fully supported” based on fish contaminant monitoring in 2005 and 2006. 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 composite samples of fillets from channel catfish and white crappie in 2005 had generally low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.92 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. Levels of primary contaminants in the composite sample of white crappie fillets were as follows: mercury: 0.12 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. The level of mercury in the sample of channel catfish fillets, however, exceeds the IDNR/IDPH trigger level of 0.30 ppm for a one meal per week consumption advisory. According to the IDNR/IDPH advisory protocol, two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow up sampling was conducted in 2006. The level of mercury in channel catfish was 0.186 ppm. The level of mercury in largemouth bass was 0.174 ppm. Both of these levels were below the trigger level for a fish consumption advisory, therefore Little River Lake is assessed as “fully supporting” the fish consumption uses.
