Three Mile Lake
Union County, Iowa880 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Three Mile Lake. Here is what has been measured.
- Eutrophic
- 46 ft max depth
- Public access
Three Mile Lake in Union County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 2.7 ft visibility. Phosphorus: 43 µg/L. Chlorophyll-a (algae): 28.4 µg/L. Surface area: 880 acres.
Free interactive depth-contour map of Three Mile Lake, reaching a maximum surveyed depth of 48 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Three Mile Lake is a 880-acre productive, nutrient-rich eutrophic lake in Union County, Iowa with an estimated average depth of about 46 feet. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 5 other monitored lakes in Union County, Three Mile Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-06-26. Methodology: how these readings are compared.
Three Mile Lake covers about 880 acres in Union County. Vrbo is where to look for cabins and lake homes around Three Mile Lake, and Booking.com and Expedia search hotels near the lake for your dates.
Swimming conditions
Readings onlyBacteria tested: exceedances
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.
Based on E. coli testing, Three Mile Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 11.1% of 9 samples across 3 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.
Whether Three Mile 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 Three Mile Lake
These are the measurements Iowa DNR publishes for Three Mile 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 2.7 ft of visibility. Phosphorus 43 µg/L. Chlorophyll-a 28.4 µg/L. TSI 62.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 43µg/L | Fair 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. | 62 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Three Mile Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Three Mile Lake typically sits around 70°F at the surface in September. Summer average is about 77°F. Usually warmest in Jul (about 81°F) and coldest in Sep (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 28 field readings (2010–2023) via the EPA Water Quality Portal. See the full Three Mile Lake water temperature breakdown →
Lake Details
Max depth
~46 ft est.
Surface area
880 acres
Public access
Yes
Listed by Iowa DNR
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Three Mile Lake.
Lake Size & Watershed
Watershed (drainage) area
36 sq mi
HydroLAKES / HydroSHEDS
Shoreline
4.5 mi
HydroLAKES / HydroSHEDS
Elevation
1,145 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Stays via Stay22
Stays near Three Mile Lake
Compare lakeside cabins, hotels, and vacation rentals near Three Mile Lake in Union 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 Three Mile Lake are listed below.
Top-rated places to stay near Three Mile Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Planning a trip? Cabins and lodging at Three Mile Lake → · more Iowa lake trips
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Fishing Three Mile Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Phosphorus
Improving-1.35 µg/L/yr4 years
Chlorophyll-a
Improving-3.06 µg/L/yr5 years
Reservoir Info (USACE NID)
Three Mile Lake is a man-made reservoir impounded by the Three Mile Reservoir Dam (completed 1995), built primarily for flood risk reduction on the THREE MILE CREEK; earth-type dam, 63 ft tall and 1,850 ft long.
- Surface area
- 880 ac
- Normal storage
- 14,091 ac-ft
- Max storage
- 29,950 ac-ft
- Drainage area
- 36.3 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
All listed purposes: Flood Risk Reduction;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IA02944 · Operator website
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Three Mile Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Three Mile Lake Campground-StpAfton · 0.6 mi away · NPDES IA0074594Recent violation
- Afton City Park SplashpadAfton · 3.1 mi away · NPDES IA0052182Recent violation
- Afton City Of StpAfton · 4 mi away · NPDES IA0041831
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 Union County
Frequently asked questions about Three Mile Lake
Where is Three Mile Lake?
- Three Mile Lake is a lake in Union County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Three Mile Lake?
- Three Mile Lake in Union County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 2.7 ft visibility. Phosphorus: 43 µg/L. Chlorophyll-a (algae): 28.4 µg/L. Surface area: 880 acres.
Is Three Mile Lake safe to swim in?
- Based on E. coli testing, Three Mile Lake frequently exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 11.1% of 9 samples across 3 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Three Mile Lake is safe to swim in today is a call for Iowa's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Three Mile Lake?
- Three Mile Lake typically sits around 70°F at the surface in September, from 28 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Three Mile Lake?
- No published bathymetric survey covers Three Mile Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 46 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 880 acres.
Can I fish at Three Mile Lake?
- Public access to Three Mile Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Iowa's fish and wildlife agency, so check its current regulations before you go.
Explore Three Mile Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Iowa's top lakes, each with its readings
Iowa's cleanest lakes, ranked on agency measurements
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Eutrophic Lakes in Iowa
Compare Three Mile Lake With Nearby Lakes
Where this data comes from
51 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX51 samples · 2020–2024
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)
Lake size & watershed from HydroLAKES (HydroSHEDS)