Seminole-Mills Lake
Seminole County, FloridaView mapDirections
Florida DEP publishes the water-quality measurements for Seminole-Mills Lake. Here is what has been measured.
- Mesotrophic
- Impaired · pH / acidity
Seminole-Mills Lake in Seminole County, Florida has water-quality measurements published by Florida DEP, shown here as reported. Water clarity: 6.3 ft visibility. Phosphorus: 17 µg/L.
Seminole-Mills Lake is a mesotrophic lake in Seminole County, Florida. Overall water quality is declining over recent sampling years. Compared to the 121 other monitored lakes in Seminole County, Seminole-Mills Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, FDEP, last sampled 2022-08-17. 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. Seminole-Mills Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for pH / acidity. Check local advisories before you swim.
Whether Seminole-Mills Lake is safe to swim in today is a call for the Florida Department of Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Seminole-Mills Lake
These are the measurements Florida DEP publishes for Seminole-Mills Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 6.3 ft. Phosphorus 17 µg/L. TSI 48.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 6.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 17µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 48 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Fishing Seminole-Mills Lake
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Worsening+4.25 µg/L/yr5 years
EPA Impairment Status
Seminole-Mills Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4C).
Causes of impairment
Designated uses not supporting: Aquatic life.
Source: EPA ATTAINS assessment unit FL3003A · Official waterbody report
Nearby Lakes in Seminole County
Frequently asked questions about Seminole-Mills Lake
Where is Seminole-Mills Lake?
- Seminole-Mills Lake is a lake in Seminole County, Florida. Its water-quality measurements are published by Florida DEP and shown on this page as reported.
What is the water quality of Seminole-Mills Lake?
- Seminole-Mills Lake in Seminole County, Florida has water-quality measurements published by Florida DEP, shown here as reported. Water clarity: 6.3 ft visibility. Phosphorus: 17 µg/L.
Is Seminole-Mills Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Seminole-Mills Lake is listed impaired under Clean Water Act §303(d) (IR 4C) for pH / acidity. Check local advisories before you swim.
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Where this data comes from
105 measurements from 3 monitoring stations, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- FLORIDA LAKEWATCH
21FLKWAT_WQX105 samples · 2020–2022
Monitoring station identifiers (3)
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