School Lake
Chisago County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for School Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Impaired biota (cause unknown)
- Public access
School Lake in Chisago County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 7.9 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 1.8 µg/L.
School Lake is a mesotrophic lake in Chisago County, Minnesota. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 29 other monitored lakes in Chisago County, School Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-19. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. School Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), mercury. Check local advisories before you swim.
Whether School Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for School Lake
These are the measurements Minnesota PCA publishes for School Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 7.9 ft. Phosphorus 20 µg/L. Chlorophyll-a 1.8 µg/L. TSI 44.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 7.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 20µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.8µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 44 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about School Lake
Answers come straight from the public measurements and survey records on this page.
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Fishing School Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Improving-11.17 µg/L/yr6 years
Chlorophyll-a
Improving-11.14 µg/L/yr6 years
EPA Impairment Status
School Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life, Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN13-0041-02 · Official waterbody report
Nearby Lakes in Chisago County
Frequently asked questions about School Lake
Where is School Lake?
- School Lake is a lake in Chisago County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of School Lake?
- School Lake in Chisago County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 7.9 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 1.8 µg/L.
Is School Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. School Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), mercury. Check local advisories before you swim.
Can I fish at School Lake?
- Public access to School Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
105 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
MNPCA105 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Secchi Transparency Tube, 100 cm
- 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
- Analysis of Chlorophyll in Periphyton and Plankton
Monitoring station identifiers (2)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database