Jefferson Lake
Jefferson Lake in Le Sueur County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 86.5 µg/L. Chlorophyll-a (algae): 72 µg/L. Surface area: 700 acres.
- Clarity
- 2 ft
- Mean depth
- ~42 ft est.
- Area
- 700 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Jefferson Lake →
Next lake in Le Sueur County
Jefferson Lake is a 700-acre productive, nutrient-rich eutrophic lake in Le Sueur County, Minnesota with an estimated average depth of about 42 feet. Water quality is graded F based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 12 other monitored lakes in Le Sueur County, Jefferson Lake ranks #10 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-11-14. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyAlgae risk
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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Very murky, less than 2 ft of visibility. Phosphorus level: 86.5 µg/L. Chlorophyll-a: 72 µg/L. Trophic State Index: 69.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | Not graded |
| Phosphorus | 86.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 72 µg/L | Poor |
| Trophic State Index (TSI) | 69 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Jefferson Lake
Compare lakeside cabins, hotels, and vacation rentals near Jefferson Lake in Le Sueur 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 Jefferson Lake are listed below.
Top-rated places to stay near Jefferson 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 |
|---|---|
| Average Depth | ~42 ft est. |
| Surface Area | 700 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Jefferson Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Jefferson Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Jefferson Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fish Stocking History — HenryFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — HenryPublic 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 | → Stable | +0.009 m/yr | 6 |
| Phosphorus | ↓ Declining | +19.5 µg/L/yr | 2 |
| Chlorophyll-a | ↓ Declining | +19.43 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Jefferson Lake is a man-made reservoir impounded by the Lake Jefferson (completed 1938), built primarily for recreation on the BIG CANNON RIVER - TR; gravity-type dam, 9 ft tall and 15 ft long.
- Surface area
- 700 ac
- Normal storage
- 18,544 ac-ft
- Max storage
- 25,489 ac-ft
- Drainage area
- 16.3 sq mi
- Hazard class
- Low
- Owner
- MNDNR-Trails
Source: USACE National Inventory of Dams, NID ID MN00155 · Operator website
EPA Impairment Status
Jefferson 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 MN40-0092-04 · Official waterbody report · Matched by proximity (0.78 km)
County Ranking
Ranked #10 of 13 lakes in Le Sueur County
Nearby Lakes With Higher Grades
Jefferson Lake holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Le Sueur County
Frequently asked questions about Jefferson Lake
What is the water quality grade for Jefferson Lake?
- Jefferson Lake in Le Sueur County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 86.5 µg/L. Chlorophyll-a (algae): 72 µg/L. Surface area: 700 acres.
Is Jefferson Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Jefferson Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 72 µg/L. Always check local health department advisories before swimming.
How deep is Jefferson Lake?
- No published bathymetric survey covers Jefferson Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 42 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 700 acres.
Explore Jefferson Lake across LakeGrade
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Where this data comes from
336 measurements from 10 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
MNPCA336 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (10)
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