Hickory Grove Lake IA 03-SSK-950
Story County S24T83NR22W 2.5 mi SW of Colo.
- Cycle
- 2026
- Current Phase
- Public Comment
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Eutrophic
- Trend
- Stable
- Created
- 10/27/2025 3:09:45 PM
- Updated
- 1/8/2026 8:23:59 AM
The Class A1 use remains assessed as “not supported” due to levels of indicator bacteria that exceeded Iowa’s water quality standard and aesthetically objectionable conditions caused by non-algal turbidity. The Class BLW use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data. Note: A TMDL for indicator bacteria E. coli at Hickory Grove Lake was prepared by DNR and approved by EPA in June 2020. Because not all of the section 303(d) impairments identified for the current assessment/listing cycle (Turbidity) are addressed in the TMDL, this waterbody remains in Category 5a (impaired; TMDL required) for the current assessment/listing cycle.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 WQ CY 2022-2024 22850001 Hickory Grove Lake (maximum water depth) Class A1 - Indicator Bacteria: No Data. See previous 2020 assessments for results. 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 22850001 6 9 / 3 7.72 9.01 8.47 1 3 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 22850001 6 Chlorophyll a TSI 9 / 3 50 72 62 NO EVALUATED FULL 22850001 6 Secchi TSI 9 / 3 46 86 60 NO EVALUATED FULL 22850001 6 Total Phosphorus TSI 9 / 3 54 92 61 NA NA NA 22850001 6 Fixed suspended solids 9 / 3 1.7 5 2 NA NA NA Although the index value for Secchi is below the impairment threshold of 65 for this assessment cycle, Hickory Grove Lake was listed as partially supporting its Class A1 uses due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Secchi must be 63 or below and a monitored assessment before it can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Hickory Grove Lake will remain listed as "not supported" for the 2026 assessment/listing cycle. Class BLW - Binomial 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 22850001 6 Dissolved Oxygen 9 / 3 7.4 13.2 9.9 0 NA / NA 3 NO MONITORED FULL 22850001 6 pH 9 / 3 7.72 9.01 8.47 1 NA / NA 3 NO MONITORED FULL 22850001 6 Temperature 9 / 3 18.2 26.5 23.5 0 NA / NA 3 NO MONITORED FULL 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 22850001 6 4 10.9401 94.05% 8.349 54.46% NO EVALUATED NA Class BLW - Toxic Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations >1 Acute / Chronic Violation Assessment Type Support Level 22850001 6 Ammonia 9 / 3 0.228 0.08 0.03 0 / 0 NO EVALUATED FULL
Class HH - Previous fish tissue monitoring results were removed based on the age of the data