Big Hollow Lake is a 178-acre productive, nutrient-rich eutrophic lake in Des Moines County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Des Moines County, Big Hollow Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-16. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Big Hollow Lake routinely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 28.6% of 7 samples across 2 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Iowa’s current beach and health-department advisories before swimming.
Water Quality Grade: F, Very Poor
Very murky, less than 1.8 ft of visibility. Chlorophyll-a: 46 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.8 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 46 µg/L | F |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 178 acres |
Where to stay near Big Hollow Lake
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Fishing Big Hollow Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.01 m/yr | 4 |
| Chlorophyll-a | ↓ Declining | +2.75 µg/L/yr | 4 |
Water Temperature
Big Hollow Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Sep (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 23 field readings (2011–2023) via the EPA Water Quality Portal. See the full Big Hollow Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Big Hollow Lake, reaching a maximum surveyed depth of 44 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #1 of 2 lakes in Des Moines County
Cleaner Lakes Within 30 Miles
Big Hollow Lake holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Des Moines County
Explore Big Hollow Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Big Hollow Lake is a man-made reservoir impounded by the Big Hollow Dam (completed 2008), built primarily for recreation on the Big Hollow Creek; earth-type dam, 60 ft tall and 795 ft long.
- Surface area
- 178 ac
- Normal storage
- 3,046 ac-ft
- Max storage
- 5,942 ac-ft
- Drainage area
- 7.5 sq mi
- Hazard class
- Significant
- Owner
- Des Moines County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA03551 · Operator website
EPA Impairment Status
Big Hollow Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 02-ICD-6496 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Big Hollow Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- United States Gypsum Company - MediapolisMediapolis · 3.7 mi away · NPDES IA0063606Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-16
Monitoring stations: 1