Klamath River algae bloom status

Klamath River algae bloom history

California's Water Boards hold 16 bloom reports for Klamath River going back to 2017. Reports came in during 5 of the 10 years since then, with the busiest year being 2023 (10 reports).

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.

Reports have fallen in the last three years compared with the three before.

That puts Klamath River in the top 15% of the 318 California lakes on this site for the number of years with blooms.

When do algae blooms happen at Klamath River?

At Klamath River, reports are most often logged in January, July and August.

Unusually, about 63% of reports here fall between November and February, so blooms aren't only a summer problem at Klamath River. 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 Klamath River algae reports

Recent reports came from 11 different locations around Klamath River, including below Indian Creek, Tree of Heaven Campground and below Happy Camp (RM 101.3; Baseline). 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 Klamath River 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 5 different years here, take particular care at Klamath River in January, July and August.

• 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

• Iron Creek19 km away, 16 reports, last in 2022
• Iron Gate Reservoir19 km away, 3 reports, last in 2023
• Copco Reservoir28 km away, 21 reports, last in 2023
• Lake Shastina42 km away, 4 reports, last in 2026
• Scott River44 km away, 8 reports, last in 2024

All Siskiyou County lakes with algae reports

Questions about Klamath River

Is there algae in Klamath River right now?

There are no bloom reports for Klamath River in the last 30 days of California's data. The most recent was a bloom report on 4 August 2026 at below Indian Creek. 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 Klamath River?

The most recent entry in California's data is from 4 August 2026 at below Indian Creek: a bloom report.

Has Klamath River had toxic algae before?

Yes. Blooms are recorded in 5 of the 10 years from 2017 to 2026, most often in January, July and August.

Can dogs swim in Klamath River?

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 Klamath River 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.