East Lake (Osceola) IA 04-LDM-1065
Clarke County S16T72NR25W 0.5 mi E of Osceola.
- Assessment Cycle
- 2018
- Release Status
- Final
- Data Collection Period
- Overall IR Category
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 3/14/2019 2:00:04 PM
- Updated
- 3/14/2019 2:13:31 PM
The Class A1 (primary contact recreation) uses of East Lake are assessed (monitored) as "not supported" due to poor water transparency, aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH. he Class B(LW) (aquatic life) uses are assessed (monitored) as "not supported" due to violations of the Class A1,B(LW) criterion for pH.Fish consumption uses remain “not assessed.” Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau.
For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of East Lake are assessed (monitored) as "not supported" due to poor water transparency, aesthetically objectionable conditions caused by algae blooms and due to frequent violations of the state criterion for pH based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 70, 68, and 85 respectively for East Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place East Lake in between the Eutrophic and the Hypereutrophic categories. These values suggest 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 data show 3 violations of the Class A1 criterion for pH in 15 samples (20%).According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, East Lake will remain listed for the 2018 cycle as "not supported" its Class A1 uses due to pH. Data from the 2012-2016 ISU lake survey suggest a moderate population of cyanobacteria exists at East Lake. These data show that cyanobacteria comprised 45% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (15.9 mg/L) was ranked 71st of the 138 lakes sampled. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake. NOTE: A TMDL for algae and turbidity for East Lake was completed by DNR and approved by EPA in 2008. Thus, these impairments are moved from IR Category 5a (impaired; TMDL required) to Category 4a (impaired; TMDL approved). Because not all the impairments identified for this lake are covered by this TMDL (pH), this lake remains in IR Category 5a.