Three Mile Slough algae bloom status

Three Mile Slough algae bloom history

California's Water Boards hold 3 bloom reports for Three Mile Slough going back to 2021. Reports came in every year since then.

None of these reports led to a formal Caution, Warning or Danger advisory. They were logged as reported blooms or awareness signs, often from members of the public.

Blooms have been recorded every year for the last 3 years in the data.

When do algae blooms happen at Three Mile Slough?

At Three Mile Slough, reports are most often logged in January and September.

Unusually, about 67% of reports here fall between November and February, so blooms aren't only a summer problem at Three Mile Slough. 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 Three Mile Slough algae reports

Recent reports came from 2 different locations around Three Mile Slough, including near San Joaquin River and near San Joaquin River (TSL). 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 California results mean

California recommends one of three advisory levels when a bloom is checked, matched to the signs posted at the shore.

Caution

Toxins may be present. Stay away from scum and keep pets and livestock from drinking the water.

Warning

Toxins are at higher levels. No swimming, and keep children and pets away from the water.

Danger

High toxin levels. Stay out of the water and off the shore until further notice.

Bloom reported

A bloom was reported, often by a member of the public, without a formal advisory level.

Is Three Mile Slough 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 3 different years here, take particular care at Three Mile Slough in January and September.

• 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

• Sevenmile Slough2 km away, 3 reports, last in 2021
• Sacramento River5 km away, 13 reports, last in 2025
• False River6 km away, 4 reports, last in 2023
• Mokelumne River10 km away, 4 reports, last in 2023
• Sherman Lake10 km away, 2 reports, last in 2022

All Sacramento County lakes with algae reports

Questions about Three Mile Slough

Is there algae in Three Mile Slough right now?

There are no bloom reports for Three Mile Slough in the last 30 days of California's data. The most recent was a bloom report on 17 January 2023 at near San Joaquin River. California's data is checked every day, so for today's conditions check the California HABs Portal map and the signs at the shore.

When was the last algae bloom at Three Mile Slough?

The most recent entry in California's data is from 17 January 2023 at near San Joaquin River: a bloom report.

Has Three Mile Slough had toxic algae before?

Yes. Blooms are recorded every year from 2021 to 2023, most often in January and September.

Can dogs swim in Three Mile Slough?

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 Three Mile Slough 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.