Unionville Lake
Putnam County, Missouri75 acresView mapDirections
Missouri DNR publishes the water-quality measurements for Unionville Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Algal growth
- 42 ft max depth
- Public access
- Limited data
Unionville Lake in Putnam County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Water clarity: 1.6 ft visibility. Phosphorus: 129.5 µg/L. Chlorophyll-a (algae): 57.5 µg/L. Surface area: 75 acres.
Unionville Lake is a 75-acre highly nutrient-loaded hypereutrophic lake in Putnam County, Missouri with an estimated average depth of about 42 feet. 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. Methodology: how these readings are compared.
What Unionville Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyLimited data
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. Unionville Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
Whether Unionville Lake is safe to swim in today is a call for the Missouri Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Unionville Lake
These are the measurements Missouri DNR publishes for Unionville 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 1.6 ft of visibility. Phosphorus 129.5 µg/L. Chlorophyll-a 57.5 µg/L. TSI 72.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 130µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 57.5µg/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. | 72 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Unionville Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Unionville Lake typically sits around 77°F at the surface in August. Summer average is about 78°F. Usually warmest in Jul (about 78°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (56°F) to its warmest (78°F).
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 →
Lake Details
Max depth
~42 ft est.
Surface area
75 acres
Public access
Yes
Listed by Missouri DNR
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Missouri has not published bathymetry for Unionville Lake.
Lake Size & Watershed
Watershed (drainage) area
26 sq mi
HydroLAKES / HydroSHEDS
Shoreline
19.4 mi
HydroLAKES / HydroSHEDS
Elevation
971 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.
Recreation & Access
- Lake Mahoney (Unionville)Public
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Unionville Lake
Compare lakeside cabins, hotels, and vacation rentals near Unionville Lake in Putnam County, Missouri — 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 Unionville Lake are listed below.
Top-rated places to stay near Unionville Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Planning a whole trip? See where to stay at Missouri’s top lakes →
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Fishing Unionville Lake
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
Designated uses not supporting: Aquatic life.
Source: EPA ATTAINS assessment unit MO_7154.00 · Official waterbody report
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.
Nearby Lakes in Putnam County
Frequently asked questions about Unionville Lake
Where is Unionville Lake?
- Unionville Lake is a lake in Putnam County, Missouri. Its water-quality measurements are published by Missouri DNR and shown on this page as reported.
What is the water quality of Unionville Lake?
- Unionville Lake in Putnam County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Water clarity: 1.6 ft visibility. Phosphorus: 129.5 µg/L. Chlorophyll-a (algae): 57.5 µg/L. Surface area: 75 acres.
Is Unionville Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Unionville Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth. Check local advisories before you swim.
What is the water temperature of Unionville Lake?
- Unionville Lake typically sits around 77°F at the surface in August, from 12 EPA Water Quality Portal field readings (2010–2020). That is a typical value for the month, not a live reading.
How deep is Unionville Lake?
- No published bathymetric survey covers Unionville Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 42 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 75 acres.
Are there boat ramps on Unionville Lake?
- Unionville Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lake Mahoney (Unionville). Public access is listed as yes.
Can I fish at Unionville Lake?
- Unionville Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Missouri's fish and wildlife agency, so check its current regulations before you go.
Explore Unionville Lake across LakeQuality
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Hypereutrophic Lakes in Missouri
Where this data comes from
20 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC20 samples · 2020
Analytical methods
- Depth, Secchi disk in meters
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory