Mill Creek Lake is a 40-acre productive, nutrient-rich eutrophic lake in O'Brien County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Water clarity is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 1 other monitored lakes in O'Brien County, Mill Creek Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-09. Grade methodology: LakeGrade methodology.
Watch Mill Creek Lake water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 3 ft of visibility. Chlorophyll-a: 36.1 µg/L. Trophic State Index: 64.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 36.1 µg/L | F |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 40 acres |
| Public Access | Yes |
Where to stay near Mill Creek Lake
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Fishing Mill Creek Lake
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.042 m/yr | 4 |
| Chlorophyll-a | ↑ Improving | -7.21 µg/L/yr | 4 |
Water Temperature
Mill Creek Lake averages about 75°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Jun (about 70°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 26 field readings (2010–2023) via the EPA Water Quality Portal. See the full Mill Creek Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Mill Creek Lake, reaching a maximum surveyed depth of 14 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #2 of 2 lakes in O'Brien County
Cleaner Lakes Within 30 Miles
Mill Creek Lake holds Grade F. 4 nearby lakes hold higher grades.
- DDog Creek LakeO'Brien County · 10.8 mi · Higher grade (F → D)
- DStolley Pit LakeClay County · 27 mi · Higher grade (F → D)
- DSpring LakeCherokee County · 17.9 mi · Higher grade (F → D)
- DGustafson LakeBuena Vista County · 27.3 mi · Higher grade (F → D)
Nearby Lakes in O'Brien County
Explore Mill Creek 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)
Mill Creek Lake is a man-made reservoir impounded by the Mill Creek Lake Dam (completed 1934), built primarily for recreation on the COLE CREEK; earth-type dam, 29 ft tall and 622 ft long.
- Surface area
- 40 ac
- Normal storage
- 125 ac-ft
- Max storage
- 500 ac-ft
- Drainage area
- 5.44 sq mi
- Hazard class
- Low
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA00837 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mill Creek Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Paullina City Of StpPaullina · 0.7 mi away · NPDES IA0032352Recent 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-09
Monitoring stations: 1