Assessment Comments

Assessment is based on: (1) results of the statewide survey of Iowa lakes conducted from 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 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 “partially supported” due to aesthetically objectionable conditions caused by poor water clarity related to algal blooms and inorganic suspended solids.   The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to 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 2009-2012 by Iowa State University (ISU), (2) results of the statewide ambient lake monitoring program conducted in 2008 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, 2010, 2012, and current (2014) assessment/listing cycle (algae and turbidity) are addressed by the TMDL, this waterbody remains in IR Category 4a (impaired; TMDL approved).

EXPLANATION: For the 2014 reporting cycle, the Class A1 (primary contact recreation) uses for East Lake are assessed (monitored) as “partially 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 2008-2012 (approximately 14 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 69, and 86 respectively for East Lake.   According to Carlson (1977) the Secchi depth and chlorophyll a values place East Lake in between the eutrophic and hypereutrophic categories, while the total phosphorus value places East Lake in the hypereutrophic category.   These values suggest high levels of chlorophyll a and suspended algae in the water, poor water transparency, and extremely high levels of phosphorus in the water column.  

The levels of inorganic suspended solids at this lake were high and suggest that non-algal turbidity contributes to the impairment at this lake.   The median level of inorganic suspended solids in East Lake (10.1 mg/L) and ranked 109th of the 134 lakes sampled by the ISU and UHL programs.

Data from the 2008-2012 ISU and UHL surveys suggest a large population of cyanobacteria exists at East Lake, which contributes to the aesthetically objectionable conditions at this lake.   These data show that cyanobacteria comprised 63% of the phytoplankton wet mass at this lake.   The median cyanobacteria wet mass (22.0 mg/L) and ranked 80th of the 134 lakes sampled.  

The Class B(LW) (aquatic life) uses are assessed (evaluated) as “partially supported” due to algae blooms and poor water quality that put the lake at risk for a fish kill based on information from the IDNR Fisheries bureau.   The ISU and UHL lake surveys data from 2008-2012 suggest "full support" (monitored) or the Class B(LW) uses.  Data collected  show no violations of the Class B(LW) criteria for ammonia in 14 samples or dissolved oxygen in 14 samples.   The data show 3 violations of the criterion for pH in 14 samples (21%).  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 pH.Based on IDNR’s assessment methodology 2 consecutive assessment/listing cycles without significantly greater than 10% of the samples violating the criterion are necessary to propose delisting based on pH violations.   Because violations of the pH criteria were not significantly greater than 10% for the 2012 assessment/listing cycle or the current (2014) assessment/listing cycle the pH impairment for East Lake is suggested for delisting.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.