Twin Lake
Twin Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 78 µg/L. Chlorophyll-a (algae): 16 µg/L.
- Clarity
- 2.5 ft
- Typical in August
- 74°F
- Max depth
- ~31 ft est.
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- No
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Twin Lake →
Next lake in Isanti County
Twin Lake is a productive, nutrient-rich eutrophic lake in Isanti County, Minnesota with an estimated average depth of about 31 feet. Water quality is graded D 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, Twin Lake ranks #9 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. 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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.5 ft of visibility. Phosphorus level: 78 µg/L. Chlorophyll-a: 16 µg/L. Trophic State Index: 63.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 78 µg/L | Poor |
| Chlorophyll-a (Algae) | 16 µg/L | Poor |
| Trophic State Index (TSI) | 63 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Twin Lake
Compare lakeside cabins, hotels, and vacation rentals near Twin 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Twin Lake are listed below.
Top-rated places to stay near Twin Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Twin Lake typically sits around 74°F at the surface in August. Summer average is about 75°F. Usually warmest in Jun (about 76°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 69 field readings (2017–2025) via the EPA Water Quality Portal. See the full Twin Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~31 ft est. |
| Average Depth | ~10 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Minnesota has not published bathymetry for Twin 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 Twin Lake
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.59 m/yr | 6 |
| Phosphorus | ↓ Declining | +2.56 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.4 µg/L/yr | 6 |
EPA Impairment Status
Twin 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
County Ranking
Ranked #9 of 17 lakes in Isanti County
Nearby Lakes With Higher Grades
Twin Lake holds Grade D. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Isanti County
Frequently asked questions about Twin Lake
What is the water quality grade for Twin Lake?
- Twin Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 78 µg/L. Chlorophyll-a (algae): 16 µg/L.
Is Twin Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Twin Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 16 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Twin Lake?
- Twin Lake typically sits around 74°F at the surface in August, from 69 EPA Water Quality Portal field readings (2017–2025). That is a typical value for the month, not a live reading.
How deep is Twin Lake?
- No published bathymetric survey covers Twin Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 31 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Twin Lake across LakeGrade
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Where this data comes from
172 measurements from 2 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
MNPCA172 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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