Hoffman Lake
Hoffman Lake in Isanti County, Minnesota has a water quality grade of A (Excellent). Water clarity: 3.7 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 3.6 µg/L.
- Clarity
- 3.7 ft
- Typical in August
- 75°F
- Mean depth
- ~10 ft est.
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- No
Next lake in Isanti County
Hoffman Lake is a mesotrophic lake in Isanti County, Minnesota with an estimated average depth of about 10 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 16 other monitored lakes in Isanti County, Hoffman Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. Grade methodology: LakeGrade methodology.
Watch Hoffman Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyLow algae
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)
Murky, only visible to about 3.7 ft. Phosphorus level: 15 µg/L. Chlorophyll-a: 3.6 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.7 ft | Not graded |
| Phosphorus | 15 µg/L | Good |
| Chlorophyll-a (Algae) | 3.6 µg/L | Good |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Hoffman Lake
Compare lakeside cabins, hotels, and vacation rentals near Hoffman Lake in Isanti 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 Hoffman 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 →
Water Temperature
Hoffman Lake typically sits around 75°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 77°F) and coldest in May (about 65°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 39 field readings (2017–2025) via the EPA Water Quality Portal. See the full Hoffman Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~10 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Hoffman 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 Hoffman Lake
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.647 m/yr | 6 |
| Phosphorus | ↓ Declining | +2.16 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.26 µg/L/yr | 6 |
EPA Impairment Status
Hoffman Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN30-0004-00 · Official waterbody report · Matched by proximity (1.91 km)
County Ranking
Ranked #5 of 17 lakes in Isanti County
Nearby Lakes in Isanti County
Frequently asked questions about Hoffman Lake
What is the water quality grade for Hoffman Lake?
- Hoffman Lake in Isanti County, Minnesota has a water quality grade of A (Excellent). Water clarity: 3.7 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 3.6 µg/L.
Is Hoffman Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Hoffman Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 3.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Hoffman Lake?
- Hoffman Lake typically sits around 75°F at the surface in August, from 39 EPA Water Quality Portal field readings (2017–2025). That is a typical value for the month, not a live reading.
How deep is Hoffman Lake?
- No published bathymetric survey covers Hoffman Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 10 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Hoffman Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Isanti County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Rum River Watershed, ranked by water quality
Moderate nutrients, good water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Hoffman Lake
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Where this data comes from
88 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA88 samples · 2020–2025
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder