East Lake (Osceola) IA 04-LDM-1065
Clarke County S16T72NR25W 0.5 mi E of Osceola.
- Assessment Cycle
- 2022
- Release Status
- Final
- Data Collection Period
- Overall IR Category
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 12/28/2021 8:58:05 AM
- Updated
- 2/4/2022 7:17:04 AM
Assessment Summary
The Class A1 use was assessed (monitored) as "not supported" due to poor water transparency. The Class BLW use was assessed (evaluated) as "WINOFI" due to excessive nutrient loading to the water column and impacts from organic enrichment. All other designated uses were “not assessed.” NOTE: A TMDL for algae and turbidity for East Lake was completed by DNR and approved by EPA in 2008. Thus, these impairments were moved from IR Category 5a (impaired; TMDL required) to Category 4a (impaired; TMDL approved). Because all the impairments identified for this lake are covered by this TMDL, this lake remains in IR Category 4a.
Assessment Explanation
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2020 22200001 East
Lake Osceola
Class A1 - Indicator Bacteria: No Data Class A1 - pH: Site ID Data Source ID # Samples / # Years Minimum Value Maximum Value Mean Value # Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22200001 6 15 / 5 6.7 9.1 8.2 1 4 NO Monitored Full Class A1 - Lake TSI's: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation? Assessment Type Support Level 22200001 6 Chlorophyll a TSI 15 / 5 36 88 59 NO Monitored Full 22200001 6 Secchi TSI 15 / 5 47 83 67 YES Monitored Not 22200001 6 Total Phosphorus TSI 15 / 5 63 100 87 NA NA NA 22200001 6 Inorganic suspended solids 15 / 5 0.3 8 3.1 NA NA NA DNR's assessment methodology indicates that at least two
assessment/listing cycles with a TSI value less than or equal to 63 are
necessary to suggest de-listing of an impairment. The chlorophyll a
TSI value for the 2002 assessment listing cycle was 67, which based on DNR's
assessment/listing methodology indicated an impairment based on the narrative
criteria protecting against aesthetically objectionable conditions. Because the
TSI value for the 2020 assessment/listing cycle was less than the trigger of 65
(2020 listing for chlorophyll a was 60), and because the TSI value for the
current listing cycle is 59, based on DNR's methodology, these values
suggest "full support" of the Class A1 use protecting against
aesthetically objectionable conditions and the impairment (4a) for chlorophyll
a is suggested for delisting for the 2022 assessment/listing cycle. Class BLW - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value # Violations # Acute / Chronic Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22200001 6 Ammonia 15 / 5 0.0003 0.447 0.1 NA 0 / 0 4 NO Monitored Full 22200001 6 Dissolved Oxygen 14 / 5 3.6 11.3 6.9 3 NA / NA 4 NO Monitored Full 22200001 6 pH 15 / 5 6.7 9.1 8.2 1 NA / NA 4 NO Monitored Full 22200001 6 Temperature 15 / 5 17.1 28.8 24.1 0 NA / NA 4 NO Monitored Full Note: The Class BLW use was assessed (evaluated) as “WINOFI”
due to algae blooms and poor water quality that put the lake at risk for a fish
kill based on information from the DNR Fisheries bureau. Class BLW - Lake Planktonic Cyanobacteria: Site ID Data Source ID # Samples Maximum Cyanobacteria Wet Mass Maximum Cyanobacteria % Composition Median Cyanobacteria Wet Mass Median Cyanobacteria % Composition Median Cyanobacteria Concentration = 75th Percentile Assessment Type Support Level 22200001 6 6 19.54 89.0% 3.82 3.5% NO Evaluated NA
Class HH: No Data
Assessment Key Dates
| 5/23/2016 | Non-fixed Monitoring Start Date |
| 9/8/2020 | Non-fixed Monitoring End Date |
| 5/14/2008 | TMDL Completed |
Methods
| 120 | Surveys of fish and game biologists/other professionals |
| 222 | Non-fixed-station monitoring (conventional during key seasons and flows) |
| 340 | Primary producer surveys (phytoplankton/periphyton/macrophyton) |