Lake South
Lake South in St. Johns County, Florida has a water quality grade of D (Nutrient-rich). Water clarity: 1.6 ft visibility. Phosphorus: 78 µg/L.
- Clarity
- 1.6 ft
- Typical in August
- 86°F
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Lake South →
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Lake South is a productive, nutrient-rich eutrophic lake in St. Johns County, Florida. Water quality is graded D based on 1 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 6 other monitored lakes in St. Johns County, Lake South ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, FDEP, last sampled 2024-12-02. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyBacteria advisory
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 1.6 ft of visibility. Phosphorus level: 78 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 78 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake South
Compare lakeside cabins, hotels, and vacation rentals near Lake South in St. Johns 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 grade measures nutrients and algae, not lodging — cabins and rentals around Lake South are listed below.
Top-rated places to stay near Lake South
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Lake South → · more Florida lake trips
Water Temperature
Lake South typically sits around 86°F at the surface in August. Summer average is about 84°F. Usually warmest in Jul (about 87°F) and coldest in Jan (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 20 field readings (2017–2024) via the EPA Water Quality Portal. See the full Lake South water temperature breakdown →
Recreation & Access
- Guana River Recreation Area - River Access RampPublic
- Guana River Recreation Area - Dam Site - Lake Access RampPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake South
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +17.97 µg/L/yr | 5 |
EPA Impairment Status
Lake South is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit FL2320 · Official waterbody report · Matched by proximity (2.44 km)
County Ranking
Ranked #1 of 7 lakes in St. Johns County
Nearby Lakes With Higher Grades
Lake South holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in St. Johns County
Frequently asked questions about Lake South
Where is Lake South?
- Lake South is a lake in St. Johns County, Florida. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake South?
- Lake South in St. Johns County, Florida has a water quality grade of D (Nutrient-rich). Water clarity: 1.6 ft visibility. Phosphorus: 78 µg/L.
Is Lake South safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Lake South has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
What is the water temperature of Lake South?
- Lake South typically sits around 86°F at the surface in August, from 20 EPA Water Quality Portal field readings (2017–2024). That is a typical value for the month, not a live reading.
Are there boat ramps on Lake South?
- Lake South has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Guana River Recreation Area - River Access Ramp, Guana River Recreation Area - Dam Site - Lake Access Ramp. Public access is listed as yes.
Explore Lake South across LakeQuality
Planning a trip around Castillo de San Marcos?
Lake South is about 9 miles from Castillo de San Marcos National Monument. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Castillo de San Marcos →More Florida Lake Rankings
Other Grade D Lakes in Florida
Eutrophic Lakes in Florida
Where this data comes from
70 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Submitting organization not recorded for these samples70 samples · 2020–2024
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
Named boat-access points from the USGS National Boat Ramps inventory