Geode Lake IA 03-SKU-896
Henry County S36T70NR5W 4 mi. SW of Danville.
- 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 3:09:43 PM
- Updated
- 11/24/2025 2:25:01 PM
The Class A1 use was assessed (monitored) as "not supported" due to aesthetically objectionable conditions caused by non-algal turbidity. The Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. The Class HH (fish consumption) use remains assessed (monitored) as “not supported” (IR 5a) based on fish tissue sampling data and due to the issuance of a fish consumption advisory at this lake. Note: A TMDL for bacteria and pH at Geode Lake was prepared by DNR and approved by EPA in 2009. Because not all of the Section 303(d) impairments identified for this assessment/listing cycle (mercury and turbidity) are addressed by the TMDL, this waterbody remains in IR Category 5a (impaired; TMDL required) for the current 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 21440001 Geode
Lake Beach
Iowa DNR 6 WQ CY 2021-2024 22290001 Lake
Geode
Iowa DNR 6 FT See Below 1070 Lake
Geode E of
Lowell 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 21440001 6 15/0/15 21 NA 26 NO 1 / 4 NA 0 / 4 NO MONITORED FULL Lake Geode was assessed as "not supported" for the
2006 assessment/listing cycle due to frequent violations of the state Class A1
criterion for pH. Based on DNR’s assessment methodology the current
assessment/listing cycles must have fewer violations of the criterion based on
the minimum required by the 10% Rule to propose removal from category 4 pH. There were less than 10% of the samples
exceeding the single-sample maximum criterion for the
2026assessment/listing cycle. Therefore, the impairment for pH is
suggested for removal from category 4 for the 2026 assessment/listing cycle. 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 22290001 6 12 / 4 7.66 9.99 8.51 2 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 22290001 6 Chlorophyll a TSI 12 / 4 30 78 63 NO MONITORED FULL 22290001 6 Secchi TSI 12 / 4 52 73 66 YES MONITORED NOT 22290001 6 Total Phosphorus TSI 12 / 4 49 81 62 NA NA NA 22290001 6 Fixed suspended solids 12 / 4 1.7 9 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 22290001 6 Dissolved Oxygen 12 / 4 3.6 11.6 8.1 1 NA / NA 4 NO MONITORED FULL 22290001 6 pH 12 / 4 7.66 9.99 8.51 2 NA / NA 4 NO MONITORED FULL 22290001 6 Temperature 12 / 4 21.9 28.1 24.4 0 NA / NA 4 NO MONITORED FULL Lake Geode was assessed as "not supported" for the
2006 assessment/listing cycle due to frequent violations of the state Class BLW
criterion for pH. Based on DNR’s assessment methodology the current assessment/listing
cycles must have fewer violations of the criterion based on the minimum
required by the 10% Rule to propose removal from category 4 pH There were less
than 10% of the samples exceeding the single-sample maximum criterion for the
2026assessment/listing cycle. Therefore, the impairment for pH is
suggested for removal from category 4 for the 2026 assessment/listing cycle. 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 22290001 6 5 26.3211 99.96% 20.0533 98.34% 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 22290001 6 Ammonia 12 / 4 0.213 0.05 0.03 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 22290001 6 Inorganic nitrogen (nitrate and nitrite) 11 / 4 0.05 4.41 1.34 0.24 0 NO MONITORED FULL 22290001 6 pH 12 / 4 7.66 9.99 8.51 8.58 2 NO MONITORED FULL
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) 1070 fillet 2009 largemouth bass 5 NA 0.437
1070 shoulder 2009 snapping turtle 2 NA 0.284 0.03 0.09 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.”