Union Lake
Wright County, Minnesota93 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Union Lake. Here is what has been measured.
- Eutrophic
- Impaired · Mercury
- 35 ft max depth
- Public access
Union Lake in Wright County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 5.5 ft visibility. Phosphorus: 23.5 µg/L. Chlorophyll-a (algae): 9.9 µg/L. Maximum depth: 35 ft. Surface area: 92.93 acres.
Minnesota DNR's Standard Survey on July 24, 2017 caught 0.75 walleye per gill net at Union Lake. DNR survey details →
Union Lake is a 93-acre productive, nutrient-rich eutrophic lake in Wright County, Minnesota with a maximum depth of 35 feet. Overall water quality is declining over recent sampling years. The lake supports 15 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 50 other monitored lakes in Wright County, Union Lake ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-10. Methodology: how these readings are compared.
What Union Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Fishing15 species recorded
- Deep water35 ft surveyed max depth
Swimming conditions
Readings onlyModerate algae
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. Union Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
Whether Union Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Union Lake
These are the measurements Minnesota PCA publishes for Union Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.5 ft. Phosphorus 23.5 µg/L. Chlorophyll-a 9.9 µg/L. TSI 52.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 23.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 9.9µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 52 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Union Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Union Lake typically sits around 59°F at the surface in September. Summer average is about 59°F. Usually warmest in Aug (about 61°F) and coldest in May (about 53°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (53°F) to its warmest (61°F).
Typical surface water temperature by month, from 260 field readings (2010–2025) via the EPA Water Quality Portal. See the full Union Lake water temperature breakdown →
Minnesota DNR's Standard Survey on July 24, 2017 caught 0.75 walleye per gill net at Union Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Union Lake’s water-quality measurements separately, and the water-quality trend over 3 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
15 surveys on file from MN DNR Fisheries. Most recent: 2022-05-31 (Targeted Survey).
15 surveys on file · most recent 2022-05-31 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 38.06 | 2–8 in 2022-05-31 | 0.2 lb |
| Black Crappie | 9.46 | 3–12 in 2022-05-31 | 0.23 lb |
| Yellow Perch | 6.90 | 5–7 in 2017-07-24 | 0.1 lb |
| Black Bullhead | 6.34 | 7–12 in 2017-07-24 | 0.51 lb |
| Largemouth Bass | 4.66 | 3–20 in 2017-07-24 | 1.21 lb |
| Yellow Bullhead | 4.02 | 8–12 in 2017-07-24 | 0.61 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Bluegill
Black Crappie
Yellow Perch
Black Bullhead
From the 2022-05-31 survey
Union is a small-sized lake (93 acres) located southwest of the City of South Haven in Wright County. Union has 1.5 miles of shoreline and a maximum depth of 35 feet. A state-owned public access with a cement boat ramp and a very small amount of parking is present on the south shore. Water clarity is typically fair to…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Union Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — UnionFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Union (2022)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — UnionPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
35 ft
Surface area
93 acres
Shoreline
1.5 mi
Littoral zone
29%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
1 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,030 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Union LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Union Lake
Compare lakeside cabins, hotels, and vacation rentals near Union Lake in Wright County, Minnesota — 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.
Top-rated places to stay near Union Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Union Lake
Water quality readings over time
3 seasons of samples on record (2020–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
Phosphorus
Worsening+7 µg/L/yr2 years
Chlorophyll-a
Worsening+2.82 µg/L/yr2 years
EPA Impairment Status
Union Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN86-0298-00 · Official waterbody report
Nearby Lakes in Wright County
Frequently asked questions about Union Lake
Where is Union Lake?
- Union Lake is a lake in Wright County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Union Lake?
- Union Lake in Wright County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 5.5 ft visibility. Phosphorus: 23.5 µg/L. Chlorophyll-a (algae): 9.9 µg/L. Maximum depth: 35 ft. Surface area: 92.93 acres.
Is Union Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Union Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
What is the water temperature of Union Lake?
- Union Lake typically sits around 59°F at the surface in September, from 260 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Union Lake?
- Union Lake has a maximum depth of 35 feet. The lake covers 92.93 acres.
What fish are in Union Lake?
- Fish species found in Union Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, channel catfish, common carp, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. Union Lake is located in Wright County, Minnesota.
What did the DNR fisheries survey find at Union Lake?
- Minnesota DNR's Standard Survey on July 24, 2017 caught 0.75 walleye per gill net at Union Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Union Lake’s water-quality measurements separately, and the water-quality trend over 3 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Are there boat ramps on Union Lake?
- Union Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Union Lake. Public access is listed as yes.
Can I fish at Union Lake?
- Union 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 Minnesota's fish and wildlife agency, so check its current regulations before you go.
Explore Union Lake across LakeQuality
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Where this data comes from
40 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA40 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory