Mill Creek Lake
O'Brien County, Iowa40 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Mill Creek Lake. Here is what has been measured.
- Eutrophic
Mill Creek Lake in O'Brien County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 3 ft visibility. Phosphorus: 62 µg/L. Chlorophyll-a (algae): 28.4 µg/L. Surface area: 40 acres.
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. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyAlgae risk
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Mill Creek Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Mill Creek Lake
These are the measurements Iowa DNR publishes for Mill Creek Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 3 ft of visibility. Phosphorus 62 µg/L. Chlorophyll-a 28.4 µg/L. TSI 63.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 62µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 28.4µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 63 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Mill Creek Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (70°F) to its warmest (81°F).
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
Surface area
40 acres
No bathymetric survey has been published for Mill Creek Lake, so its depth is not documented here.
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 readings cover 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 Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Mill Creek Lake
Water Quality Trend: Worsening
Based on 4 years of monitoring (2021–2024).
Water clarity
Worsening4 years
Phosphorus
Worsening+14.15 µg/L/yr4 years
Chlorophyll-a
Improving-3.64 µg/L/yr4 years
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.
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. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Mill Creek Lake?
- Mill Creek Lake in O'Brien County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. 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?
- Nutrient and algae readings are 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 lakes in Iowa
Other 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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)