Mill Creek Lake
O'Brien County, Iowa40 acresView mapDirections
Nutrients and algae run above the regional average.
↑ up from F at the last regrade
- Eutrophic
- #2 of 2 in the county
Mill Creek Lake in O'Brien County, Iowa has a water quality grade of D (Nutrient-rich). Water clarity: 3 ft visibility. Phosphorus: 62 µg/L. Chlorophyll-a (algae): 28.4 µg/L. Surface area: 40 acres.
- Clarity
- 3 ft
- Typical in September
- 73°F
- Area
- 40 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
Stays via Stay22
Stays near Mill Creek Lake
Compare lakeside cabins, hotels, and vacation rentals near Mill Creek Lake in O'Brien County, Iowa — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Mill Creek Lake are listed below.
Top-rated places to stay near Mill Creek Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Watch Mill Creek Lake’s letter
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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.
Mill Creek Lake is a 40-acre productive, nutrient-rich eutrophic lake in O'Brien County, Iowa. Water quality is graded D based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. 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: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 3 ft of visibility. Phosphorus 62 µg/L. Chlorophyll-a 28.4 µg/L. TSI 63. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 62 µg/L | Poor |
| Chlorophyll-a (Algae) | 28.4 µg/L | Poor |
| Trophic State Index (TSI) | 63 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Mill Creek Lake typically sits around 73°F at the surface in September. Summer average is about 75°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 40 acres |
No bathymetric survey has been published for Mill Creek Lake, so its depth is not documented here.
Fishing Mill Creek Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.042 m/yr | 4 |
| Phosphorus | ↓ Declining | +14.15 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -3.64 µg/L/yr | 4 |
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.
County Ranking
Ranked #2 of 2 lakes in O'Brien County
Nearby Lakes With Higher Grades
Mill Creek Lake holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in O'Brien County
Frequently asked questions about Mill Creek Lake
Where is Mill Creek Lake?
- Mill Creek Lake is a lake in O'Brien County, Iowa. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mill Creek Lake?
- Mill Creek Lake in O'Brien County, Iowa has a water quality grade of D (Nutrient-rich). Water clarity: 3 ft visibility. Phosphorus: 62 µg/L. Chlorophyll-a (algae): 28.4 µg/L. Surface area: 40 acres.
Is Mill Creek Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Mill Creek Lake?
- Mill Creek Lake typically sits around 73°F at the surface in September, from 26 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Mill Creek Lake across LakeQuality
More Iowa Lake Rankings
Other Grade D Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
52 measurements from 1 monitoring station, 2021–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX52 samples · 2021–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- In-Vitro Determination of Chlorophyll
- ISU modification of APHA 2130-B
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)