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), and (3) information from the IDNR Fisheries Bureau.
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 clarity related to algal blooms and inorganic suspended solids. High levels of pH that exceed state criteria also contribute to the impairment at this lake. The Class B(LW) (aquatic life) uses are assessed (monitored) as “partially supported” due to high levels of pH that exceed state criteria, excessive nutrient loading to the water column, and impacts from organic enrichment. Fish consumption uses remain “not assessed.” 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), and (3) information from the IDNR Fisheries Bureau.
NOTE: A TMDL for algae and turbidity for East Lake was completed by IDNR and approved by EPA in 2008. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (algae and turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2008 reporting cycle, the Class A1 (primary contact recreation) uses for East Lake are assessed (monitored) as “not supported” based on results from the ISU statewide survey of lakes and the UHL ambient lake monitoring program. Using the median values from these surveys from 2002 through 2006 (approximately 27 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 73, 71, and 86 respectively for East Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place East Lake in the hypereutrophic category. These values suggest very high levels of chlorophyll a and suspended algae in the water, very poor water transparency, and extremely high levels of phosphorus in the water column.
The levels of inorganic suspended solids at this lake were relatively high and suggest that non-algal turbidity contributes to the impairment at this lake. The median level of inorganic suspended solids in East Lake (7.0 mg/L) was the 39th highest median of the 132 lakes sampled by the ISU and UHL programs.
Data from the 2002-2006 ISU and UHL surveys suggest a large population of cyanobacteria exists at East Lake, which may contribute to the aesthetically objectionable conditions at this lake. These data show that cyanobacteria comprised 79% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (29.7 mg/L) was also the 40th highest of the 132 lakes sampled.
The Class B(LW) (aquatic life) uses are assessed as “partially supported” due to violations of the Class B(LW) criteria for pH. Information from the IDNR Fisheries Bureau also suggests that the aquatic life uses are “partially supported” due to algae blooms and poor water quality that put the lake at risk for a fish kill. The ISU and UHL lake surveys data from 2002-2006 show no violations of the Class B(LW) criteria for ammonia in 20 samples. The data show three violations of the criterion for dissolved oxygen in 26 samples (12%). Based on IDNR’s assessment methodology, however, these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the aquatic life uses due to dissolved oxygen at this lake. Five of the 25 pH samples violated the Class A1,B(LW) criterion for pH. Based on IDNR’s methodology these violations are significantly greater than 10% of the samples and therefore suggest an impairment (partial support/monitored) of the Class A1,B(LW) uses of East Lake. These violations, however, likely reflect the excessive primary productivity at East Lake and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
