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B

Lower Prior Lake

Scott County, MinnesotaMesotrophic

Lower Prior Lake comes in at a B on the grading rubric — a respectable showing for a Minnesota lake of its size and depth. With clarity and phosphorus scored, the sub-grades cluster within a letter of each other, pointing to stable conditions rather than one specific stressor.

A TSI near 48 places Lower Prior Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. Lower Prior Lake is unusually deep for Minnesota at 60 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 956 acres, Lower Prior Lake fits the Minnesota median for monitored lakes, with 14.7 miles of shoreline. Lower Prior Lake ranks 3 of 17 in Scott County, putting it in the upper tier of locally monitored lakes.

Zebra mussel presence at Lower Prior Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at Lower Prior Lake, one of 15 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. The lake has a partial ice record — 19 observed ice-outs, centered near Apr 4. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-24. Grade methodology: LakeGrade methodology.

Reviewed by LakeQuality Editorial Team · Updated

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Swimming Safety

Good for swimming, clear water with low algae levels

Water Quality Grade: B, Good

Moderate clarity, visible to about 9.5 ft. Phosphorus level: 26.8 µg/L. Trophic State Index: 48.

MetricValueGrade
Water Clarity (Secchi Depth)9.5 ftC
Phosphorus26.8 µg/LB
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)48Mesotrophic

Moderate nutrients, good water quality

Lake Details

CharacteristicValue
Maximum Depth60 ft
Surface Area956.16 acres
Shoreline Length14.7 mi
Littoral Zone39%
Public AccessYes

Fish Species

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

Click a species to see all Minnesota and Wisconsin lakes where it is found.

→ Best fishing times for Lower Prior Lake (14-day solunar calendar)

→ Is it safe to eat fish from Lower Prior Lake? (mercury & PFAS guide)

Lower Prior Lake fishing regulations (limits, seasons, special rules)

Invasive & Introduced Species

Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.

Eurasian watermilfoilzebra mussel

Water Quality Trend: Declining

Based on 5 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Declining-0.148 m/yr5
Phosphorus Declining+1 µg/L/yr3
See year-by-year chart →

Ice Season

Historical ice data from Minnesota DNR (62 observations).

Typical Ice-Out
Apr 4
Typical Ice-In
Dec 1

Estimated open water season: 241 days

EarliestLatest
Ice-Out2024-03-03 (2024)2018-05-02 (2018)
Ice-In1986-11-15 (1986)2001-12-26 (2001)

Most recent ice-out: 2025-03-25

Location

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County Ranking

Ranked #3 of 17 lakes in Scott County

Cleaner Lakes Within 30 Miles

Lower Prior Lake holds Grade B. One nearby lake has a higher grade.

See full comparison →

Nearby Lakes in Scott County

DNR Fisheries Survey Summary

17 surveys on file from MN DNR Fisheries. Most recent: 2025-09-09 (Targeted Survey).

Top Species by Catch Rate

SpeciesAvg CPUEAvg Weight
Bluegill24.770.17 lb
SFS19.32
Bluntnose Minnow12.85
Largemouth Bass7.390.54 lb
GOS6.290.17 lb
Yellow Bass3.400.82 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

363 fish · 28 in · 2024-07-17
1035202345678

Largemouth Bass

21 fish · 517 in · 2024-07-17
1050567891011121314151617

GOS

2 fish · 77 in · 2021-07-20
2107

Yellow Bass

127 fish · 714 in · 2024-07-17
422107891011121314

From the 2025-09-09 survey

Minnesota DNR Fisheries IBI program staff conducted an assessment of lakeshore habitat on Lower Prior Lake on September 9th 2025, following the Score the Shore survey protocols. The assessment consisted of 119 survey sites evenly spaced 200 meters around the lake. Assessments were made in three habitat zones:…

Source: MN DNR LakeFinder Fisheries Lake Survey

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Lower Prior Lake. 3 reports on file.

Reservoir Info (USACE NID)

Lower Prior Lake is a man-made reservoir impounded by the Prior Lake on the Minnesota River-TR; gravity-type dam, 12 ft tall and 8 ft long.

Surface area
1,056 ac
Normal storage
1,760 ac-ft
Drainage area
35 sq mi
Hazard class
Low
Owner
MNDNR

Source: USACE National Inventory of Dams, NID ID MN01328 · Operator website

EPA Impairment Status

Lower Prior Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).

Causes of impairment

Impaired biota (cause unknown)Mercury

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit MN70-0026-00 · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Lake details from Minnesota DNR LakeFinder

Ice data from Minnesota DNR Climate

Most recent sample: 2024-09-24

Monitoring stations: 3