Johns Lake algae bloom status

Johns Lake algae bloom history

Florida's Department of Environmental Protection sampled Johns Lake 5 times between 2022 and 2025. Staff saw a bloom on 2 visits (40%).

Microcystin, the most common algal toxin, was not detected in any sample tested here.

When do algae blooms happen at Johns Lake?

About 100% of reports fall between May and September, when warm, calm, sunny weather lets blue-green algae multiply.

Blooms can appear, move with the wind and fade within hours or days, so the time of year is only a guide.

Recent Johns Lake algae reports

Recent reports came from 5 different locations around Johns Lake, including Johns Lake - W of Scrub Point Preserve, Johns Lake - Near Burch Island Ct and Johns Lake - Deer Island N Cove. A bloom in one cove or beach doesn't mean the whole lake is affected, and conditions can differ a short distance away.

What the Florida results mean

Florida records whether staff saw a bloom at each visit and, when a sample is tested, how much microcystin it contained.

Bloom seen

Staff saw a bloom at the sampling site, and no toxin was found or tested.

Toxin detected

Microcystin, a liver toxin made by blue-green algae, was found in the sample.

8 µg/L or more

At or above the level where the US EPA recommends swimming advisories.

Is Johns Lake safe for dogs?

Dogs are at the greatest risk from toxic algae. They swallow water while swimming, eat scum on the shore and lick algae off their fur afterwards, and a small amount can kill a dog within hours.

• Keep your dog on a lead near water that looks green, scummy, foamy or discoloured, and away from algae washed up on the shore.
• If your dog gets in, rinse it straight away with clean water and don't let it lick its coat.
• Call a vet immediately if your dog vomits, drools, has diarrhoea, staggers, shakes or seems weak after being near the water.

Health effects of toxic algae

Blue-green algae (cyanobacteria) can produce toxins that affect the liver, nervous system and skin. Swallowing water during a bloom can cause stomach pain, vomiting and diarrhoea. Skin contact can cause rashes, and breathing spray from the water can irritate the eyes, nose and throat. Children are at higher risk because they are smaller and more likely to swallow water.

How to spot a bloom

Toxic blooms can look like pea soup, spilled paint or green streaks on the surface, and they can also be blue, brown, white or red. Scum often collects along the shore downwind. If you can't see your feet in knee-deep water, or you aren't sure, stay out.

Don't drink untreated lake water, and don't boil it to make it safe: boiling doesn't destroy algal toxins. If you feel unwell after contact with the water, contact a doctor or Poison Control on 1-800-222-1222.

Nearby lakes with algae reports

• Lake Roberts7 km away, 20 reports, last in 2025
• Lake Speer7 km away, 20 reports, last in 2023
• Caywood Pond7 km away, 12 reports, last in 2023
• Lake Hancock8 km away, 4 reports, last in 2025
• Cypress Lake9 km away, 12 reports, last in 2024

All Orange County lakes with algae reports

Questions about Johns Lake

Is there algae in Johns Lake right now?

Florida's most recent sample from Johns Lake, on 20 August 2025 at Johns Lake - W of Scrub Point Preserve, found no visible bloom and no microcystin toxin was detected. Florida publishes its data in yearly batches, so for today's conditions check the DEP Algal Bloom Dashboard and the signs at the shore.

When was the last algae bloom at Johns Lake?

The most recent entry in Florida's data is from 20 August 2025 at Johns Lake - W of Scrub Point Preserve: a sample with no bloom seen.

Has Johns Lake had toxic algae before?

Yes. Blooms are recorded in 2 of the 4 years from 2022 to 2025.

Can dogs swim in Johns Lake?

Keep dogs out of the water whenever a bloom is reported or the water looks green, scummy or discoloured. Dogs are the animals most often killed by algal toxins because they swallow water and lick their fur. If your dog swims in water that might have algae, rinse it with clean water and call a vet if it vomits, drools, staggers or seems weak.

Can you eat fish caught in Johns Lake during a bloom?

If you keep fish caught during a bloom, health agencies advise removing the guts and liver and rinsing the fillets in clean water before cooking, because toxins collect most in the organs. Some agencies advise not eating fish from an active bloom at all, so follow local guidance.