Lake Weir algae bloom status

Lake Weir algae bloom history

Florida's Department of Environmental Protection sampled Lake Weir 33 times between 2018 and 2025. Staff saw a bloom on 24 visits (73%).

The highest microcystin result recorded here was 0.33 µg/L, below the US EPA swimming advisory level of 8 µg/L.

Blooms have been recorded every year for the last 7 years in the data.

That puts Lake Weir 3rd of the 293 Florida lakes on this site for the number of years with blooms.

When do algae blooms happen at Lake Weir?

At Lake Weir, reports are most often logged in May, July and December.

Unusually, about 29% of reports here fall between November and February, so blooms aren't only a summer problem at Lake Weir. Some of this reflects when the lake is monitored, not just when blooms happen.

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

Recent Lake Weir algae reports

Recent reports came from 8 different locations around Lake Weir, including Lake Weir - Hope Boat Ramp, Lake Weir - Carney Island Boat Ramp and Lake Weir - N Shore. 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 Lake Weir 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. With blooms recorded in 7 different years here, take particular care at Lake Weir in May, July and December.

• 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.

Read the full guide to toxic algae and dogs: symptoms, what to do in the first minutes and how vets treat it.

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

• Ocklawaha River9 km away, 2 reports, last in 2023
• Lake Yale23 km away, 28 reports, last in 2025
• Lake Griffin23 km away, 9 reports, last in 2025
• Harris Bayou25 km away, 15 reports, last in 2025
• Lake Harris27 km away, 16 reports, last in 2024

All Marion County lakes with algae reports

Questions about Lake Weir

Is there algae in Lake Weir right now?

Florida's most recent sample from Lake Weir, on 28 July 2025 at Lake Weir - Hope Boat Ramp, found a 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 Lake Weir?

The most recent entry in Florida's data is from 28 July 2025 at Lake Weir - Hope Boat Ramp: a bloom seen during sampling.

Has Lake Weir had toxic algae before?

Yes. Blooms are recorded in 7 of the 8 years from 2018 to 2025, most often in May, July and December.

Can dogs swim in Lake Weir?

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 Lake Weir 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.