Upper Prior Lake
Upper Prior Lake in Scott County, Minnesota has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 38.7 µg/L. Chlorophyll-a (algae): 8.8 µg/L. Maximum depth: 50 ft. Surface area: 386.26 acres.
- Clarity
- 5 ft
- Typical in August
- 66°F
- Max depth
- 50 ft
- Area
- 386 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 5
- Open water
- 240 days
Next lake in Scott County
Upper Prior Lake is a 386-acre productive, nutrient-rich eutrophic lake in Scott County, Minnesota with a maximum depth of 50 feet. Water quality is graded C based on 3 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 16 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 20 other monitored lakes in Scott County, Upper Prior Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-26. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 5 ft. Phosphorus level: 38.7 µg/L. Chlorophyll-a: 8.8 µg/L. Trophic State Index: 54.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | Not graded |
| Phosphorus | 38.7 µg/L | Fair |
| Chlorophyll-a (Algae) | 8.8 µg/L | Fair |
| Trophic State Index (TSI) | 54 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Upper Prior Lake
Compare lakeside cabins, hotels, and vacation rentals near Upper Prior Lake in Scott 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.
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Water Temperature
Upper Prior Lake typically sits around 66°F at the surface in August. Summer average is about 64°F. Usually warmest in Aug (about 66°F) and coldest in Jan (about 37°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 1,662 field readings (2010–2025) via the EPA Water Quality Portal. See the full Upper Prior Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 50 ft |
| Surface Area | 386 acres |
| Shoreline Length | 6.2 mi |
| Littoral Zone | 85% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- DewittPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Upper Prior 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
17 surveys on file from MN DNR Fisheries. Most recent: 2025-06-23 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 57.25 | — |
| Bluegill | 47.04 | 0.2 lb |
| SFS | 23.35 | — |
| Black Crappie | 14.31 | 0.23 lb |
| Yellow Perch | 6.96 | 0.19 lb |
| JND | 6.94 | — |
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.
Bluntnose Minnow
Bluegill
SFS
Black Crappie
From the 2025-06-23 survey
A targeted survey of nearshore fish species in Upper Prior Lake was conducted beginning on June 23, 2025, by Lake Biological Monitoring and Assessment (LBMA) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine,…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Upper Prior Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Upper PriorFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — Upper PriorFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Upper PriorPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.118 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.73 µg/L/yr | 6 |
| Chlorophyll-a | → Stable | +0.19 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (195 observations).
Estimated open water season: 240 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-03 (2024) | 2013-04-29 (2013) |
| Ice-In | 1991-11-06 (1991) | 2001-12-24 (2001) |
Most recent ice-out: 2025-03-24
EPA Impairment Status
Upper Prior 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 MN70-0072-00 · Official waterbody report
County Ranking
Ranked #3 of 21 lakes in Scott County
Nearby Lakes in Scott County
Frequently asked questions about Upper Prior Lake
What is the water quality grade for Upper Prior Lake?
- Upper Prior Lake in Scott County, Minnesota has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 38.7 µg/L. Chlorophyll-a (algae): 8.8 µg/L. Maximum depth: 50 ft. Surface area: 386.26 acres.
Is Upper Prior Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Upper Prior Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 8.8 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Upper Prior Lake?
- Upper Prior Lake typically sits around 66°F at the surface in August, from 1,662 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Upper Prior Lake?
- Upper Prior Lake has a maximum depth of 50 feet. The lake covers 386.26 acres.
What fish are in Upper Prior Lake?
- Fish species found in Upper Prior Lake include black bullhead, black crappie, bluegill, brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white bass, white crappie, white sucker, yellow bullhead, yellow perch. Upper Prior Lake is located in Scott County, Minnesota.
When does Upper Prior Lake thaw?
- Upper Prior Lake typically has ice-out around Apr 5. Ice typically forms around Dec 1. The open water season is approximately 240 days.
Are there boat ramps on Upper Prior Lake?
- Upper Prior Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Dewitt. Public access is listed as yes.
Explore Upper Prior 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 Scott County
Species activity outlook by water temperature and season
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Lakes in the Minnesota River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Upper Prior Lake
Other Grade C Lakes in Minnesota
Eutrophic Lakes in Minnesota
Where this data comes from
491 measurements from 3 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA491 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 4500 N C ~ Persufate Method for Total Nitrogen
- Turbidity, Nephelometric Method
Monitoring station identifiers (3)
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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate