Union Lake
Union Lake in Rice County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 3 ft visibility. Phosphorus: 375 µg/L. Chlorophyll-a (algae): 29.2 µg/L. Maximum depth: 10 ft. Surface area: 396.74 acres.
- Clarity
- 3 ft
- Typical in August
- 78°F
- Max depth
- 10 ft
- Area
- 397 acres
- Type
- Hypereutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Mar 23
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Union Lake →
Next lake in Rice County
Union Lake is a 397-acre highly nutrient-loaded hypereutrophic lake in Rice County, Minnesota with a maximum depth of 10 feet. Water quality is graded D based on 1 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 13 other monitored lakes in Rice County, Union Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-10. Grade methodology: LakeGrade methodology.
Watch Union Lake water quality
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Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 3 ft of visibility. Phosphorus level: 375 µg/L. Chlorophyll-a: 29.2 µg/L. Trophic State Index: 72.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 375 µg/L | Not graded |
| Chlorophyll-a (Algae) | 29.2 µg/L | Poor |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Union Lake
Compare lakeside cabins, hotels, and vacation rentals near Union Lake in Rice 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Union Lake are listed below.
Top-rated places to stay near Union Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Union Lake typically sits around 78°F at the surface in August. Summer average is about 77°F. Usually warmest in Jul (about 81°F) and coldest in May (about 49°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 49 field readings (2011–2025) via the EPA Water Quality Portal. See the full Union Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Union Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was very high (1,976,970 cells/mL) on July 18, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 10 ft |
| Surface Area | 397 acres |
| Shoreline Length | 5.2 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Union LakePublic
Fishing Union Lake
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 2015-07-20 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 98.02 | 0.21 lb |
| Common Carp | 56.44 | 0.48 lb |
| Black Crappie | 20.20 | 0.19 lb |
| Yellow Perch | 12.59 | 0.16 lb |
| White Sucker | 10.89 | 1.22 lb |
| Northern Pike | 10.58 | 2.4 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
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.
Black Bullhead
Common Carp
Black Crappie
Yellow Perch
From the 2015-07-20 survey
Union Lake is a 403 acre lake located in Rice County near the town of Little Chicago. A county-owned earthen access is located on the northeast side of the lake off Rice County Highway 46. Union Lake has a maximum depth of 10 feet and is placed in Lake Class 43, which includes other Waterville Area Lakes such as…
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
- —Fish Stocking History — UnionFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — UnionPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.254 m/yr | 3 |
Ice Season
Historical ice data from Minnesota DNR (12 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-02-29 (2024) | 2018-04-29 (2018) |
Most recent ice-out: 2025-03-22
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN66-0032-00 · Official waterbody report
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.
- Mndot - Heath Creek Rest AreaFaribault · 1.3 mi away · NPDES MN0069639Recent 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.
County Ranking
Ranked #2 of 14 lakes in Rice County
Nearby Lakes With Higher Grades
Union Lake holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Rice County
Frequently asked questions about Union Lake
What is the water quality grade for Union Lake?
- Union Lake in Rice County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 3 ft visibility. Phosphorus: 375 µg/L. Chlorophyll-a (algae): 29.2 µg/L. Maximum depth: 10 ft. Surface area: 396.74 acres.
Is Union Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Union Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 29.2 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Union Lake?
- Union Lake typically sits around 78°F at the surface in August, from 49 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Union Lake?
- Union Lake has a maximum depth of 10 feet. The lake covers 396.74 acres.
When does Union Lake thaw?
- Union Lake typically has ice-out around Mar 23.
Does Union Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Union Lake (clouds, ice, or an off-season gap). The most recent reading was very high (1,976,970 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
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.
Explore Union Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Rice County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Union Lake
Other Grade D Lakes in Minnesota
Hypereutrophic Lakes in Minnesota
Where this data comes from
35 measurements from 1 monitoring station, 2022–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA35 samples · 2022–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated 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)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate