Several bodies of water have been placed under health advisory in recent years due to high and potentially dangerous levels of bacteria and toxic plant life. There are sometimes problems with toxic green algae in the Lakes in Northern California. Sadly, two dogs died in 2017 in a pond in due to exposure of blue-green algae in Northern California. Officials from the California State Water Resources Control Board said that the problem was worse than ever that year.

Algae blooms are large formations of algae that can cover the surface of a body of water. Algae blooms are common in flat water, but they don’t always turn toxic. There have been a few cases of toxic algae this year but they only a few that have turned toxic.

Below you will find a list of places that have been put on the watch list because they have had toxic blue-green algae in recent years. Cyanobacteria, also known as blue-green algae, usually peaks in late July to early August, so keep your eyes peeled for this dangerous aquatic species.

For more information about what lakes have been put on the watch list and the dangers posed by toxic algae, visit the California government website.

Keep an eye out for green algae that looks like this. As stated above, it's not always toxic, but you should do your research ahead of time and call ahead to see if there has been any evidence of anything toxic.
Flickr/ Gerda Kettner
1. Shasta Lake
Shasta Lake, CA 96019, USA
Flickr/ Sister Luke
So far, Shasta Lake's green algae levels seem to be safe. In years past, however, there has been toxic algae found here. In 2016, officials were urging people to stay away from the Pit River Arm because of this very problem. Call (530) 275-1296 before you visit to double check that it's still safe. When it is, it's a fun spot for swimming in NorCal.

Read more about Shasta Lake, one of the most popular lakes in Northern California.
2. Napa County Ponds
Napa County, CA, USA
Flickr/ Rocky A
The two dogs mentioned in the intro above were swimming in ponds contaminated with toxic algae. Shallow ponds are the perfect breeding ground for this type of algae, so proceed with caution if you frequent these kinds of bodies of water around Napa County Ponds.
3. Lake Temescal
Lake Temescal, Oakland, CA 94618, USA
Flickr/ Daniel Ramirez
According to the East Bay Regional Park District, Lake Temescal is currently closed to all swimmers due to that blue-green toxic algae in NorCal that pops up from time to time. Visitors should keep dogs out of the water.

Learn about Temescal Canyon.

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4. Discovery Bay
Discovery Bay, CA, USA
Flickr/ Dave Parker
Discovery Bay often has issues with toxic algae, so it's always smart to check the status before visiting. Visitors will see Caution, Warning, and Danger signs that each mean different things. Be sure to read the fine print.

Check out more about Discovery Bay.
5. Eel River
Eel River, California, USA
Flickr/ Diane Tebault
The Eel River is historically cold and low in nutrients that algae live on. Development in the area has changed the river, but the Eel Recovery Project is working on restoring the area. They constantly monitor the algae for levels of toxins and currently have no warnings online for toxic algae, so this is a nice spot for safe swimming in NorCal now.

Find out more about things to do near the Eel River.
6. Klamath River
Klamath River, California 96044, USA
Flickr/ Linda Tanner
The Klamath River is also constantly monitored for toxic blue-green algae. There have been no studies that seem to have come up positive for it recently, but the Klamath Basin Monitoring Program advises staying away from areas where algae is visibly present as a precaution. Read more about Klamath River.
7. Lake Oroville
Lake Oroville, California, USA
Flickr/ Pat Strosahl
A while back, the State Water Control Resources Board told boaters to avoid the Middle Fork of the Feather River Arm of Lake Oroville because of toxic algae growing there. Make sure to check the status before heading out.
br> Check out more about Lake Oroville.
8. Clear Lake
Clear Lake, California, USA
Flickr/ Daniel Hartwig
Clear Lake is also being constantly monitored thanks to the previous presence of toxic algae. It's a high priority to keep toxins low at this popular and frequently visited lake, so hopefully you won't run into that green algae found in other NorCal lakes.

Read more about Clear Lake.

Interested in learning more? Watch this video so you know what to look for in the lakes in Northern California:

Algae levels and advisories fluctuate throughout the summer, so the information above is subject to change as new water samples are taken. Please follow all signs and directions at local lakes and rivers, and stay up to date on water advisories in your area.

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More to Explore

Northern California Lakes

Danielle Schwartz | June 08, 2022

What are the most beautiful lakes in Northern California?

These are the most beautiful lakes in Northern California:

  • Trinity Lake
  • Lake Almanor
  • Lake Berryessa
  • Lake Oroville

 

There are lots of gorgeous lakes in Northern California when you're looking for a lovely outdoor getaway in our region. One of your new favorites is Lake Almanor. It's a reservoir that is wonderful for boating and swimming and features some really beautiful blue water. Lake Berryessa is found in Napa County, and truly looks like it's right out of a storybook. It's the biggest lake in Northern California, and a fun place to find fellow outdoors enthusiasts.

What are the best beaches in Northern California?

The best beaches in Northern California are:

  • Trinidad State Beach
  • Greenwood Beach State Park
  • Centerville Beach
  • Enderts Beach

 

When the weather warms up and it's time to lounge by the ocean, we've got the perfect list of the best beaches in Northern California. You'll want to drive right over to Greenwood Beach State Park for its stunningly vibrant blue water. Enderts Beach has incredible cliffs that will take you to another world. And Jug Handle State Reserve is an idyllic hideaway that you will want to lounge at all day long.

What hikes in Northern California are short and sweet?

The best short and sweet hikes in Northern California are:

  • Stout Grove, Jedediah Smith State Park
  • Boy Scout Tree Trail, Jedediah Smith State Park
  • Montgomery Grove Trail, Mondocino
  • Tall Trees Grove, Redwood National Park
  • Sun Trail (OR) 6. Dipsea Trail, Muir Woods

 

If you're looking for an escape but don't have too much time, you'll find exactly what you need in these waterfalls in Northern California. You don't even need to hike to these lovely water features, so once you've made the drive, the trip is done and you can simply relax and enjoy the sound of rushing water and take in the peaceful sight of the water falling down while surrounded by bright greenery. One major highlight from this list is Horsetail Falls in Lake Tahoe. You'll be mesmerized by this incredible place.

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