Is St Johns River safe? Toxic algae status
Duval County, Florida. Harmful algal bloom (blue-green algae) reports from the Florida Department of Environmental Protection (DEP).
Data checked 24 October 2026. Florida data is published as a yearly file; current sampling is shown on the DEP dashboard.
260
sampling visits since 2017
77
visits where a bloom was seen
40 µg/L
highest microcystin result; 6 samples at or above the EPA swim level of 8 µg/L
Year by year
Each box shows visits where a bloom was seen, out of all sampling visits that year.
Reports at St Johns River are most often logged in August, September and October.
Recent reports
| Date | Location | Result |
|---|---|---|
| 16 December 2025 | St. Johns River - Shands Bridge (20030157) | No bloom seen · microcystin not detected |
| 16 December 2025 | St. Johns River - Mandarin Point (MP72) | No bloom seen · microcystin not detected |
| 13 November 2025 | St. Johns River - Shands Bridge (20030157) | Bloom seen · microcystin not detected |
| 13 November 2025 | St. Johns River - Mandarin Point (MP72) | No bloom seen · microcystin not detected |
| 27 October 2025 | St. Johns River - Shands Bridge (20030157) | Bloom seen · microcystin not detected |
| 27 October 2025 | St. Johns River - Mandarin Point (MP72) | No bloom seen · microcystin not detected |
| 14 October 2025 | St. Johns River - Shands Bridge (20030157) | Bloom seen · microcystin not detected |
| 14 October 2025 | St. Johns River - Mandarin Point (MP72) | No bloom seen · microcystin not detected |
| 1 October 2025 | St. Johns River - Arlington Marina | No bloom seen · microcystin not detected |
| 1 October 2025 | St. Johns River - Cummer Museum of Art | No bloom seen · microcystin not detected |
| 23 September 2025 | St. Johns River - Shands Bridge (20030157) | Bloom seen · microcystin not detected |
| 23 September 2025 | St. Johns River - Mandarin Point (MP72) | No bloom seen · microcystin not detected |
What the results mean
Staff saw a bloom at the sampling site. A sample may then be tested for toxins.
Microcystin, a liver toxin made by blue-green algae, was found in the sample.
At or above the level where the US EPA recommends swimming advisories for microcystins.
Dogs and toxic algae
Dogs face the greatest risk because they swallow water and lick algae off their fur. If a bloom has been reported, keep dogs out of the water and away from scum on the shore. If your dog swims in water that might have algae, rinse it with clean water straight away and call a vet if it seems unwell.
Common questions
Is St Johns River safe to swim in?
The most recent entry in Florida's published data is from 16 December 2025: no bloom seen · microcystin not detected (St. Johns River - Shands Bridge (20030157)). Blooms have been recorded at St Johns River in 6 different years, so treat green, scummy or discoloured water with caution. For current conditions, check the DEP Algal Bloom Dashboard and posted signs.
When does St Johns River get algae blooms?
In the state's records, reports are most often logged in August, September and October. Blooms are most likely in warm, calm weather, but they can appear at other times of year.
Source: Florida Department of Environmental Protection (DEP), official data. St Johns River spans Clay County, Duval County and St. Johns County; reports from all of them are combined here. This page is independent and not affiliated with the State of Florida.