Rock Creek Lake IA 03-NSK-865
Jasper County S17T80NR17W 4 mi. ENE of Kellogg.
- Cycle
- 2026
- Current Phase
- Public Comment
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 10/27/2025 3:09:42 PM
- Updated
- 11/24/2025 2:24:42 PM
The Class A1 use was assessed (monitored) as “not supported” due to aesthetically objectionable conditions due to low water clarity and algae blooms also caused an impairment at this lake. The Class BLW use was assessed (evaluated) as “not supported” based on information from the DNR Fisheries Bureau that suggested that siltation remains a problem at Rock Creek Lake. The Class C (drinking water) use was assessed as "fully supported" based on water quality monitoring data. All other designated uses are “not assessed.” Note: A TMDL for siltation and nutrients at Rock Creek Lake was prepared by DNR and approved by EPA in 2001. Because all of the Section 303(d) impairment were addressed in the TMDL, this waterbody was will move form Category 5a (impaired; TMDL required) to 4a (TMDL has been completed) for this assessment/listing cycles.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2022-2024 21500001 Rock
Creek Beach
Iowa DNR 6 WQ CY 2020-2024 22500001 Rock
Creek Max Depth
Class A1 - Indicator Bacteria: Site ID Data Source ID # Samples per Year (2022/ 2023/2024) 2022 Geometric Mean 2023 Geometric Mean 2024 Geometric Mean Violates Annual Geometric Mean? # 2022 SSM violations / SSM Violations needed for impairment # 2023 SSM violations / SSM Violations needed for impairment # 2024 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 21500001 6 14/15/11 16 21 31 NO 0 / 4 1 / 4 1 / 3 NO MONITORED FULL 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 22500001 6 23 / 5 7.6 9.1 8.6 2 5 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 22500001 6 Chlorophyll a TSI 14 / 5 51 80 76 YES MONITORED NOT 22500001 6 Secchi TSI 25 / 5 66 77 76 YES MONITORED NOT 22500001 6 Total Phosphorus TSI 14 / 5 37 89 78 NA NA NA 22500001 6 Fixed suspended solids 14 / 5 1.9 30 8.8 NA NA NA 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 22500001 6 Dissolved Oxygen 23 / 5 7.1 15.3 9.7 0 NA / NA 5 NO MONITORED FULL 22500001 6 pH 23 / 5 7.6 9.1 8.6 2 NA / NA 5 NO MONITORED FULL 22500001 6 Temperature 23 / 5 17.1 27.6 24.3 0 NA / NA 5 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 22500001 6 4 45.5586 84.11% 18.7279 66.84% YES EVALUATED WINOFI 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 22500001 6 Ammonia 14 / 5 0.8183 0.11 0.04 0 / 0 NO MONITORED FULL Class C - Binomial Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value Median Value # Violations Violates Significantly >10% Rule? Assessment Type Support Level 22500001 6 Inorganic nitrogen (nitrate and nitrite) 13 / 5 0.03 4.46 0.81 0.22 0 NO MONITORED FULL 22500001 6 pH 23 / 5 7.6 9.1 8.6 8.6 2 NO MONITORED FULL Class HH - Previous results from fish tissue results were removed based on the age of the data.