Big Hollow Lake IA 02-ICD-6496
Approximately 5 miles southwest of Mediapolis IA in S-17 T-71N R-3W Des Moines Co.
- 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
- Eutrophic
- Trend
- Stable
- Created
- 10/27/2025 3:10:40 PM
- Updated
- 1/12/2026 12:50:17 PM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2016 | Class BLW | pH | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
| 2016 | Class A1 | pH | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 use was assessed (monitored) as “not supported” due to the presence of aesthetically objectionable conditions caused by non-algal turbidity and algal blooms. The Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. The Class HH (fish consumption) use was assessed (evaluated) as "fully supported" based on turtle tissue sampling data. A TMDL for algae, turbidity, and pH at Big Hollow Lake was prepared by DNR and approved by EPA in October 2025. Because all Section 303(d) impairments are identified for the current assessment/listing cycle are addressed by the TMDL, this waterbody is placed in category 4a (impaired, TMDL approved).
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2021-2024 22290002 Big
Hollow Lake
Iowa DNR 6 FT See Below 1344 Big
Hollow Lake Big
Hollow Recreational Area Class A - 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 22290002 6 12 / 4 6.98 8.67 8.07 0 4 NO MONITORED FULL Big Hollow Lake was assessed as "not supported" for
the 2016 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 delisting 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 delisting for the 2026 assessment/listing cycle. 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 22290002 6 Chlorophyll a TSI 12 / 4 30 81 68 YES MONITORED NOT 22290002 6 Secchi TSI 12 / 4 42 74 68 YES MONITORED NOT 22290002 6 Total Phosphorus TSI 12 / 4 51 78 72 NA NA NA 22290002 6 Fixed suspended solids 12 / 4 1.7 8 2 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 22290002 6 Dissolved Oxygen 12 / 4 3.8 9.9 7.4 1 NA / NA 4 NO MONITORED FULL 22290002 6 pH 12 / 4 6.98 8.67 8.07 0 NA / NA 4 NO MONITORED FULL 22290002 6 Temperature 12 / 4 19 26.6 23.3 0 NA / NA 4 NO MONITORED FULL Big Hollow Lake was assessed as "not supported" for
the 2016 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 delisting 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 delisting 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 22290002 6 4 111.3182437 97.94% 16.02987693 67.46% 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 22290002 6 Ammonia 12 / 4 0.299 0.06 0.03 0 / 0 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) 1344 shoulder 2015 snapping turtle 3 28.3 0.16 0.02 0.06 Support Level Full