Union Lake is a productive, nutrient-rich eutrophic lake in Branch County, Michigan. Water quality is graded D based on 1 sampling years through 2022. Overall water quality is improving over recent sampling years. The lake supports 22 documented fish species including Barred fantail darter, Blackchin shiner, and Bluegill. Public access is available with 1 public boat landing. Compared to the 4 other monitored lakes in Branch County, Union Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Michigan DNR, last sampled 2022-09-20. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 3.5 ft. Trophic State Index: 59.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.5 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Union Lake
Compare lakeside cabins, hotels, and vacation rentals near Union Lake in Branch County, Michigan — 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.
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Union Lake
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.78 m/yr | 3 |
Recreation & Access
Location & Depth Map
Free interactive depth-contour map of Union Lake, reaching a maximum surveyed depth of 16 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Michigan DNR.
County Ranking
Ranked #4 of 5 lakes in Branch County
Cleaner Lakes Within 30 Miles
Union Lake holds Grade D. One nearby lake has a higher grade.
Nearby Lakes in Branch County
Explore Union Lake across LakeGrade
Fish species and top-graded lakes across Michigan
Fish species and best lakes in Branch County
Species activity outlook by water temperature and season
Where to stay at Michigan's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
Michigan's cleanest and most-polluted lakes, ranked
More Michigan Lake Rankings
Other Grade D Lakes in Michigan
St. Joseph County · Clarity: 2 ft
St. Joseph County · Clarity: 6.5 ft
St. Joseph County · Clarity: 4.5 ft
St. Joseph County · Clarity: 5 ft
Kalamazoo County · Clarity: 4 ft
Hillsdale County · Clarity: 2.5 ft
Eutrophic Lakes in Michigan
More records, surveys & data sources
EPA Impairment Status
Union Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MI040500010403-03 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Union Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Union City WwtpUnion City · 3 mi away · NPDES MI0024244Recent 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.
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: 2022-09-20
Monitoring stations: 1