Fourth Lake
Fourth Lake in Chisago County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 120 µg/L. Chlorophyll-a (algae): 51.7 µg/L.
- Typical in August
- 75°F
- Trend
- ↑ Improving
- Public access
- No
Next lake in Chisago County
Why Fourth Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Fourth Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded phosphorus and algae (chlorophyll-a), but not water clarity.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Fourth Lake is a lake in Chisago County, Minnesota. Overall water quality is improving over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2020-09-16. Grade methodology: LakeGrade methodology.
Watch Fourth Lake water quality
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Fourth Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
No clarity data. Phosphorus level: 120 µg/L. Chlorophyll-a: 51.7 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 120 µg/L | Not graded |
| Chlorophyll-a (Algae) | 51.7 µg/L | Not graded |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Fourth Lake
Compare lakeside cabins, hotels, and vacation rentals near Fourth Lake in Chisago 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 Fourth Lake
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Water Temperature
Fourth Lake typically sits around 75°F at the surface in August. Summer average is about 73°F. Usually warmest in Aug (about 75°F) and coldest in Oct (about 47°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 76 field readings (2019–2019) via the EPA Water Quality Portal. See the full Fourth Lake water temperature breakdown →
Fishing Fourth Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.113 m/yr | 2 |
| Phosphorus | ↑ Improving | -13.75 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -10.18 µg/L/yr | 2 |
EPA Impairment Status
Fourth 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 MN13-0023-00 · Official waterbody report · Matched by proximity (0.92 km)
Graded lakes near Fourth Lake
Fourth Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Chisago County
Frequently asked questions about Fourth Lake
What is the water quality grade for Fourth Lake?
- Fourth Lake in Chisago County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 120 µg/L. Chlorophyll-a (algae): 51.7 µg/L.
Is Fourth Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Fourth Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Algae concentration (chlorophyll-a) is 51.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Fourth Lake?
- Fourth Lake typically sits around 75°F at the surface in August, from 76 EPA Water Quality Portal field readings (2019–2019). That is a typical value for the month, not a live reading.
Explore Fourth Lake across LakeGrade
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Where this data comes from
2 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA2 samples · 2020
Analytical methods
- Phosphorus by Two Reagent 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