Third Lake
Third Lake in Carlton County, Minnesota has a water quality grade of A (Excellent). Water clarity: 8.5 ft visibility. Phosphorus: 21.5 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
- Clarity
- 8.5 ft
- Typical in August
- 65°F
- Type
- Mesotrophic
- Trend
- → Stable
Next lake in Carlton County
Third Lake is a mesotrophic lake in Carlton County, Minnesota. Water quality is graded A based on 2 sampling years through 2024. Water clarity is improving over recent sampling years. Compared to the 21 other monitored lakes in Carlton County, Third Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-15. Grade methodology: LakeGrade methodology.
Watch Third Lake water quality
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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)
Moderate clarity, visible to about 8.5 ft. Phosphorus level: 21.5 µg/L. Chlorophyll-a: 2.3 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.5 ft | Not graded |
| Phosphorus | 21.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.3 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Third Lake
Compare lakeside cabins, hotels, and vacation rentals near Third Lake in Carlton 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 Third Lake
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Water Temperature
Third Lake typically sits around 65°F at the surface in August. Summer average is about 65°F. Usually warmest in Jul (about 73°F) and coldest in May (about 50°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 253 field readings (2010–2021) via the EPA Water Quality Portal. See the full Third Lake water temperature breakdown →
Fishing Third Lake
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.148 m/yr | 5 |
| Phosphorus | ↓ Declining | +20.9 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | 0 µg/L/yr | 5 |
EPA Impairment Status
Third Lake is officially listed as impaired under Clean Water Act §303(d) in the 2019 EPA reporting cycle.
Causes of impairment
Source: EPA ATTAINS assessment unit FDL_122 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Third Lake under Clean Water Act (NPDES) discharge permits.
- Fond Du Lac Band Of Lake SuperiorCloquet · 0.7 mi away · NPDES MN0075017
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #2 of 22 lakes in Carlton County
Nearby Lakes in Carlton County
Frequently asked questions about Third Lake
What is the water quality grade for Third Lake?
- Third Lake in Carlton County, Minnesota has a water quality grade of A (Excellent). Water clarity: 8.5 ft visibility. Phosphorus: 21.5 µg/L. Chlorophyll-a (algae): 2.3 µg/L.
Is Third Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Third Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Third Lake?
- Third Lake typically sits around 65°F at the surface in August, from 253 EPA Water Quality Portal field readings (2010–2021). That is a typical value for the month, not a live reading.
Explore Third Lake across LakeGrade
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Moderate nutrients, good water quality
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State Parks Near Third Lake
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Where this data comes from
341 measurements from 5 monitoring stations, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Fond du Lac Band of Chippewa (MN)
FONDULAC_WQX341 samples · 2020–2024
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
- 10200 H ~ Chlorophyll a-b-c Determination
- Color, APHA Platinum-Cobalt
- For determination of Copper by the Bicinchoninate method.
Monitoring station identifiers (5)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)