North Union Lake
North Union Lake in Douglas County, Minnesota has a water quality grade of A (Excellent). Water clarity: 20.3 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 2.4 µg/L. Maximum depth: 42 ft. Surface area: 118.41 acres.
- Clarity
- 20.3 ft
- Max depth
- 42 ft
- Area
- 118 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- No
Next lake in Douglas County
North Union Lake is a 118-acre cold, clear oligotrophic lake in Douglas County, Minnesota with a maximum depth of 42 feet (5-foot average). Water quality is graded A based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. The lake supports 13 documented fish species including black crappie, bluegill, and brown bullhead. No public access — the lake is private or restricted. Compared to the 36 other monitored lakes in Douglas County, North Union Lake ranks #24 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-15. Grade methodology: LakeGrade methodology.
Watch North Union Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Crystal clear, you can see 20.3 ft down. Phosphorus level: 13.5 µg/L. Chlorophyll-a: 2.4 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20.3 ft | Not graded |
| Phosphorus | 13.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.4 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near North Union Lake
Compare lakeside cabins, hotels, and vacation rentals near North Union Lake in Douglas 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 North Union Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 42 ft |
| Average Depth | 5 ft |
| Surface Area | 118 acres |
| Shoreline Length | 4.1 mi |
| Littoral Zone | 75% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing North Union Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
7 surveys on file from MN DNR Fisheries. Most recent: 2018-08-08 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 21.40 | 0.2 lb |
| GOS | 15.12 | — |
| BKS | 10.26 | — |
| Black Bullhead | 8.12 | 1 lb |
| Yellow Bass | 7.77 | 0.67 lb |
| Pumpkinseed | 5.98 | 0.29 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.
Bluegill
Black Bullhead
Yellow Bass
Pumpkinseed
From the 2018-08-08 survey
North Union, Stony, and Lottie (Taylor) lakes form a chain of lakes between Brophy and Cowdry Lakes in Douglas County. North Union Lake is the upper or first lake in this chain of interconnected lakes. Brophy Lake discharges into North Union. North Union outlets to Stony Lake. None of these three small basins have…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for North Union Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — North UnionFisheries Lake Survey · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.022 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.83 µg/L/yr | 6 |
| Chlorophyll-a | → Stable | 0 µg/L/yr | 6 |
EPA Impairment Status
North 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 MN21-0094-00 · Official waterbody report · Matched by proximity (2.02 km)
County Ranking
Ranked #24 of 37 lakes in Douglas County
Nearby Lakes in Douglas County
Frequently asked questions about North Union Lake
What is the water quality grade for North Union Lake?
- North Union Lake in Douglas County, Minnesota has a water quality grade of A (Excellent). Water clarity: 20.3 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 2.4 µg/L. Maximum depth: 42 ft. Surface area: 118.41 acres.
Is North Union Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. North Union Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.4 µg/L. Always check local health department advisories before swimming.
How deep is North Union Lake?
- North Union Lake has a maximum depth of 42 feet and an average depth of 5 feet. The lake covers 118.41 acres.
What fish are in North Union Lake?
- Fish species found in North Union Lake include black crappie, bluegill, brown bullhead, common carp, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, yellow bullhead, yellow perch. North Union Lake is located in Douglas County, Minnesota.
Explore North Union Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Douglas County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Alexandria Lakes area
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the St. Croix Watershed, ranked by water quality
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Lakes in the Sauk River Watershed, ranked by water quality
Low nutrients, clear water, excellent for swimming
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near North Union Lake
Other Grade A Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Where this data comes from
15 measurements from 1 monitoring station, 2021–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA15 samples · 2021–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent 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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder