Little River Watershed Lake IA 05-GRA-1358
Decatur County S19T69NR25W approx 2 mi NW of Leon.
- 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 3:10:08 PM
- Updated
- 1/2/2026 9:59:46 AM
The Class A1 use remains assessed (monitored) as “not supported” due to violations of the state's water quality criteria for indicator bacteria and aesthetically objectionable conditions caused by algae blooms. The Class BLW use was assessed (monitored) as "not supported" due to violations of the class BLW criteria for dissolved oxygen. The Class BLW use was also assessed (evaluated) as "WINOFI" due to a fish kill. The Class C use was “fully supported” based on water quality monitoring data and drinking water compliance monitoring required by the DNR. The Class HH (fish consumption) use was assessed (monitored) as "not supported" based on fish tissue sampling data and due to the existence of a one meal/week mercury consumption advisory for largemouth bass on this segment. Note: A TMDL for turbidity and total phosphorus at Little River Watershed Lake was prepared for and approved by EPA in March 2014. Because not all of the impairments (indicator bacteria, chlorophyll a, dissolved oxygen, mercury) at Little River Watershed Lake were not addressed in this TMDL, it will remain listed in category 5a; impaired - TMDL needed.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2021-2024 22270001 Little
River Lake
Iowa DNR 6 FT See Below 1075 Little
River Lake W
of Leon Class A1 - Indicator Bacteria: No Data. See Historical 2018 assessment. 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 22270001 6 12 / 4 6.4 8.8 8 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 22270001 6 Chlorophyll a TSI 12 / 4 55 79 70 YES MONITORED NOT 22270001 6 Secchi TSI 12 / 4 56 70 64 NO MONITORED FULL 22270001 6 Total Phosphorus TSI 12 / 4 58 72 67 NA NA NA 22270001 6 Fixed suspended solids 12 / 4 1.9 12 3 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 22270001 6 Dissolved Oxygen 12 / 4 2 9.2 6.1 5 NA / NA 4 YES MONITORED NOT 22270001 6 pH 12 / 4 6.4 8.8 8 1 NA / NA 4 NO MONITORED FULL 22270001 6 Temperature 12 / 4 19.5 26.4 24.1 0 NA / NA 4 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 22270001 6 8 64.19088344 91.70% 8.907722497 56.41% 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 22270001 6 Ammonia 12 / 4 0.174 0.06 0.04 0 / 0 NO MONITORED FULL Class BLW - Fish Kill: The Class BLW use was assessed (evaluated) as “WINOFI” due to fish kill that occurred in May of 2023. Because the cause of the fish kill was not identified, or the fish kill was attributed to a non-pollutant cause (e.g., winterkill), the assessment type is “evaluated.” Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of waters in need of further investigation. If no additional fish kills are reported in the segment for a 5 year period, the Category will be changed from 3b to 3a (water not assessed). Details about the 2023 fish kill can be found here: https://programs.iowadnr.gov/fishkill/events/1037 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 22270001 6 Inorganic nitrogen (nitrate and nitrite) 11 / 4 0.05 0.51 0.19 0.17 0 NO MONITORED FULL 22270001 6 pH 12 / 4 6.4 8.8 8 7.9 1 NO MONITORED FULL Class C - Iowa Drinking Water Compliance Report: Compliance monitoring required by the Iowa DNR Water Supply Operations and Engineering Sections did not show violations of finished water that were caused by source water at the Leon Water Supply facility during the 2022-24 monitoring period. The violations reported were related to plant operations. The results of compliance monitoring as reported in annual compliance reports are available at the following location at the Iowa DNR’s home page: https://www.iowadnr.gov/Environmental-Protection/Water-Quality/Water-Supply-Engineering/Annual-Compliance-Report. Class HH - Fish
Tissue Sampling: Site ID Biopart Year Species # in sample / # of samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 1075 fillet 2016 channel catfish 4 59.8 0.09 0.02 0.06 1075 tissue plug 2019 largemouth bass 10 35.8 0.357
1075 tissue plug 2017 largemouth bass 3 39.3 0.357
1075 tissue plug 2016 largemouth bass 3 39.5 0.453
Support Level Not A one meal/week mercury consumption advisory for
largemouth bass exists on this segment. Based on IR Methodology, the Class HH
(fish consumption) use was assessed as “not supported.”