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), 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. 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 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), 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, and current (2012) assessment/listing cycle (algae and turbidity) are addressed by the TMDL, this waterbody remains in IR Category 4a (impaired; TMDL approved).
EXPLANATION: For the 2012 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 2006 through 2010 (approximately 22 samples), Carlson’s (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 67, 68, and 87 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 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 (6.0 mg/L) was the 42nd highest median of the 134 lakes sampled by the ISU and UHL programs.
Data from the 2006-2010 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 81% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (48.2 mg/L) was also the 35th highest of the 134 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 2006-2010 show no violations of the Class B(LW) criteria for ammonia in 22 samples. The data show 3 violations of the criterion for dissolved oxygen 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 an impairment of the aquatic life uses due to dissolved oxygen. Four of the 22 pH samples (18%) violated the Class A1,B(LW) criterion for pH. Based on IDNR’s methodology these violations are not significantly greater than 10% of the samples and therefore do not suggest an impairment of the Class A1,B(LW) uses of East Lake. East Lake was assessed as “partially supporting” in the 2010 assessment/listing cycle due to significant violations of the pH criteria. 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 this is the first assessment/listing cycle without significantly greater than 10% of the samples violating the standard, East Lake will remain assessed as "partially supported" based on the pH violations. 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.
