North Fork American River algae bloom history
California's Water Boards hold 6 bloom reports for North Fork American River going back to 2022. Reports came in during 2 of the 3 years since then, with the busiest year being 2022 (4 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.
- 2022 4 reports
- 2023 None
- 2024 2 reports
When do algae blooms happen at North Fork American River?
At North Fork American River, reports are most often logged in May, June and September.
About 83% 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 North Fork American River algae reports
Recent reports came from 6 different locations around North Fork American River, including Mississippi Bar, Ponderosa Way and North Fork American River, China Bar. A bloom in one cove or beach doesn't mean the whole lake is affected, and conditions can differ a short distance away.
| Date | Location | Result |
|---|---|---|
| 15 October 2024 | Mississippi Bar | Bloom reported |
| 16 September 2024 | Ponderosa Way | Bloom reported |
| 13 June 2022 | North Fork American River, China Bar | Bloom reported |
| 17 May 2022 | Mineral Bar | Algal mat alert sign |
| 16 May 2022 | Oregon Bar | Bloom reported |
| 16 May 2022 | Rattlesnake Bar | Bloom reported |
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 North Fork American 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.
- 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
- American River7 km away, 26 reports, last in 2025
- Lake Clementine10 km away, 9 reports, last in 2024
- Folsom Lake16 km away, 18 reports, last in 2026
- Combie Lake17 km away, 2 reports, last in 2026
- Lake Natoma24 km away, 8 reports, last in 2024
Questions about North Fork American River
Is there algae in North Fork American River right now?
There are no bloom reports for North Fork American River in the last 30 days of California's data. The most recent was a bloom report on 15 October 2024 at Mississippi Bar. 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 North Fork American River?
The most recent entry in California's data is from 15 October 2024 at Mississippi Bar: a bloom report.
Has North Fork American River had toxic algae before?
Yes. Blooms are recorded in 2 of the 3 years from 2022 to 2024, most often in May, June and September.
Can dogs swim in North Fork American 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 North Fork American 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.
About this data
This page uses official records from the California State Water Resources Control Board, which updated daily. Reports are grouped by waterbody. The site was last rebuilt on 24 October 2026.
States only test some lakes, some of the time, so a lake without a recent report hasn't necessarily been checked. This page is independent, isn't affiliated with the State of California, and isn't health advice. View the source data.