Unionville Lake is a 75-acre highly nutrient-loaded hypereutrophic lake in Putnam County, Missouri. Water quality is graded F based on 3 sampling years through 2020. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2020-08-25. Grade methodology: LakeGrade methodology.
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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 1.6 ft of visibility. Phosphorus level: 129.5 µg/L. Chlorophyll-a: 57.5 µg/L. Trophic State Index: 72.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | 129.5 µg/L | F |
| Chlorophyll-a (Algae) | 57.5 µg/L | F |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 75 acres |
| Public Access | Yes |
Where to stay near Unionville Lake
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Fishing Unionville Lake
Recreation & Access
Water Temperature
Unionville Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 78°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 12 field readings (2010–2020) via the EPA Water Quality Portal. See the full Unionville Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 1 lakes in Putnam County
Cleaner Lakes Within 30 Miles
Unionville Lake holds Grade F. 5 nearby lakes hold higher grades.
- BMilan Lake NorthSullivan County · 21.1 mi · Two grade letters higher (F → B)
- CHazel Creek Lk. LakeAdair County · 25.2 mi · Two grade letters higher (F → C)
- CHazel Creek Lk. LakeAdair County · 25.1 mi · Two grade letters higher (F → C)
- DHazel Creek Lk. East Fork LakeAdair County · 26.8 mi · Higher grade (F → D)
- FElmwood LakeSullivan County · 19.6 mi · Higher overall water quality score
Nearby Lakes in Putnam County
Explore Unionville Lake across LakeGrade
Species activity outlook by water temperature and season
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Very high nutrients, dense algae, poor clarity
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More records, surveys & data sources
Reservoir Info (USACE NID)
Unionville Lake is a man-made reservoir impounded by the Lake Mahoney Dam (completed 1941), built primarily for recreation on the TR-BLACKBIRD CREEK; earth-type dam, 30 ft tall.
- Surface area
- 75 ac
- Normal storage
- 450 ac-ft
- Max storage
- 1,204 ac-ft
- Drainage area
- 1,900 sq mi
- Hazard class
- Low
- Owner
- UNIONVILLE,MO
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID MO10382 · Operator website · Matched by proximity (0.11 km)
EPA Impairment Status
Unionville Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MO_7154.00 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Unionville Lake under Clean Water Act (NPDES) discharge permits. 3 facilities have a reported Clean Water Act violation in the past three years.
- Unionville North WwtfUnionville · 1.9 mi away · NPDES MO0054569Recent violation
- Wildflower Community WwtfUnionville · 2.1 mi away · NPDES MO0057215Recent violation
- Unionville South WwtfUnionville · 2.9 mi away · NPDES MO0026646Recent violation
- Jr Meat CompanyUnionville · 1.6 mi away · NPDES MONX00856
- Smithfield Hog Production Whitetail FarmUnionville · 4.8 mi away · NPDES MO0117421
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)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2020-08-25
Monitoring stations: 1