You May Not Want To Swim In These 8 Northern California Lakes This Summer Due To A Dangerous Discovery

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 Northern California lakes. Sadly, two dogs died in 2017 in a pond in Napa County because of exposure to toxic algae. Officials from the California State Water Resources Control Board are saying 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 the 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, click here.

Flickr/ Gerda Kettner

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.

Shasta Lake, CA 96019, 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.

Napa County, CA, 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.

Lake Temescal, Oakland, CA 94618, USA

Flickr/ Dave Parker

As of December 2021, Discover Bay in the East Bay area is officially toxic algae free, although it was another place of concern last year. Here, 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.

Discovery Bay, CA, 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.

Eel River, California, 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 this year, but the Klamath Basin Monitoring Program advises staying away from areas where algae is visibly present as a precaution. Read more about Klamath River.

Klamath River, California 96044, USA

Flickr/ Pat Strosahl

Last August, 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. They are in the clear so far this year. Check out more about Lake Oroville.

Lake Oroville, 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.

Clear Lake, California, USA

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

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 here.

The OIYS Visitor Center

Northern California Lakes

June 08, 2022

Danielle Schwartz

What are the most beautiful lakes in Northern California?

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?

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?

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.