Pinellas-Alligator Lake
Pinellas County, Florida79 acresView mapDirections
Florida DEP publishes the water-quality measurements for Pinellas-Alligator Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Impaired biota (cause unknown)
- Limited data
Pinellas-Alligator Lake in Pinellas County, Florida has water-quality measurements published by Florida DEP, shown here as reported. Water clarity: 2.2 ft visibility. Phosphorus: 158.5 µg/L. Surface area: 79 acres.
Pinellas-Alligator Lake is a 79-acre highly nutrient-loaded hypereutrophic lake in Pinellas County, Florida. Overall water quality is declining over recent sampling years. Compared to the 33 other monitored lakes in Pinellas County, Pinellas-Alligator Lake ranks #27 for water quality.
Source: EPA Water Quality Portal sampling records, FDEP, last sampled 2023-04-01. Methodology: how these readings are compared.
Swimming conditions
Readings onlyRecreation use not supported
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. Pinellas-Alligator Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Pinellas-Alligator 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 Pinellas-Alligator Lake
These are the measurements Florida DEP publishes for Pinellas-Alligator Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 2.2 ft of visibility. Phosphorus 158.5 µg/L. TSI 71.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 159µg/L | Poor 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. | 71 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Pinellas-Alligator Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Pinellas-Alligator Lake typically sits around 84°F at the surface in September. Summer average is about 86°F. Usually warmest in Aug (about 86°F) and coldest in Dec (about 56°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (56°F) to its warmest (86°F).
Typical surface water temperature by month, from 75 field readings (2010–2012) via the EPA Water Quality Portal. See the full Pinellas-Alligator Lake water temperature breakdown →
Lake Details
Surface area
79 acres
No bathymetric survey has been published for Pinellas-Alligator Lake, so its depth is not documented here.
Stays via Stay22
Stays near Pinellas-Alligator Lake
Compare lakeside cabins, hotels, and vacation rentals near Pinellas-Alligator Lake in Pinellas County, Florida — 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Pinellas-Alligator Lake are listed below.
Top-rated places to stay near Pinellas-Alligator Lake
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Fishing Pinellas-Alligator Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Phosphorus
Worsening+12.5 µg/L/yr5 years
Reservoir Info (USACE NID)
Pinellas-Alligator Lake is a man-made reservoir impounded by the Alligator Lake Weir, built primarily for flood risk reduction on the Alligator Creek; earth-type dam, 9 ft tall and 103 ft long.
- Surface area
- 79 ac
- Normal storage
- 200 ac-ft
- Max storage
- 311 ac-ft
- Drainage area
- 8 sq mi
- Hazard class
- Significant
- Owner
- PINELLAS COUNTY
All listed purposes: Flood Risk Reduction;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID FL78002 · Operator website · Matched by proximity (0.34 km)
EPA Impairment Status
Pinellas-Alligator Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life, Recreation.
Source: EPA ATTAINS assessment unit FL1574A · Official waterbody report
Nearby Lakes in Pinellas County
Frequently asked questions about Pinellas-Alligator Lake
Where is Pinellas-Alligator Lake?
- Pinellas-Alligator Lake is a lake in Pinellas County, Florida. Its water-quality measurements are published by Florida DEP and shown on this page as reported.
What is the water quality of Pinellas-Alligator Lake?
- Pinellas-Alligator Lake in Pinellas County, Florida has water-quality measurements published by Florida DEP, shown here as reported. Water clarity: 2.2 ft visibility. Phosphorus: 158.5 µg/L. Surface area: 79 acres.
Is Pinellas-Alligator Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Pinellas-Alligator Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Pinellas-Alligator Lake?
- Pinellas-Alligator Lake typically sits around 84°F at the surface in September, from 75 EPA Water Quality Portal field readings (2010–2012). That is a typical value for the month, not a live reading.
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Where this data comes from
27 measurements from 3 monitoring stations, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- FLORIDA LAKEWATCH
21FLKWAT_WQX27 samples · 2022–2023
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