If you’ve been to the beach lately you’ve likely seen an unfamiliar and unforgettable sight: algae. Lots of algae. More algae than long-term researchers have ever seen. 

The type of algae you may have experienced varies all around the lake and the extent changes week by week. What is it? What is causing it? Should you be concerned?

Attached Algae

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Earlier in the summer, the algae near the shoreline were periphyton, which are attached algae on rocks and gravel that can often appear as yellow-brown stalks. They occur around the lake every year. As these algae age in early summer, they break loose from rocks and can wash up on beaches. What was different this year were the vast areas covered by these algae and the thickness of the growth.  

Using monthly helicopter flights, the UC Davis Tahoe Environmental Research Center has been able to track the extent and seasonal changes of periphyton. 

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The causes of periphyton “blooms” are still not fully understood. Nutrients from runoff and groundwater are a contributor. Low lake levels, such as we have in 2022, are also believed to play a role. The periphyton are not harmful, but they decrease our enjoyment of the lake and its shore. 

Filamentous Algae

The second kind of algae seriously impacting the lake this summer are metaphyton. These stringy, filamentous, green algae were increasingly found around the shoreline starting in mid-summer and are the most noticeable type of algae. They leave the water looking like pea soup, cling to swimmers, and easily wash up on beaches where they slowly decompose, producing putrid odors. 

The cause of the green algae is directly linked to the presence of invasive Asian clams. The clams appeared at Lake Tahoe 15 years ago and have spread across the south and east shores up to Sand Harbor. Wherever the clams appear, the algae follow soon after. They are not harmful, but they do put a damper on Tahoe’s clear water and clean beaches.

Harmful Algal Blooms

The third kind of “algae” impacting Tahoe beaches are freshwater harmful algal blooms, or more simply, HABs. Toxic algal blooms are not actually algae, but tiny organisms called cyanobacteria that release toxins when they die. These have rarely been seen at Tahoe’s beaches, but the frequency of warning signs and potential sightings is increasing. In other lakes where they occur intensely, they produce thick algal scums, noxious odors, have the potential to cause severe skin irritation, and to even be toxic. 

HABs are very serious, and agencies in both California and Nevada keep a close watch on them. The California Water Board maintains an interactive map showing routine monitoring locations and event-reports: bit.ly/ca-hab-map. In Nevada, suspected HABs are tracked by the state’s Department of Environmental Protection: bit.ly/nv-hab. 

Should you be concerned?

Yes. Aside from the risk of toxic harmful algal blooms, the growing intensity and spread of other types of algae is changing Lake Tahoe in a way that benefits no one. Whether you enjoy going to the beach, earn your living in the tourism industry, or simply love Tahoe, these changes put much of this at risk.

What needs to be done?

If we had all the answers, then the problem would not exist. But we don’t. It has only been in the last few years that scientists have been able to demonstrate how to measure the algae’s extent using helicopters and drones. Quantifying the size of the problem is an important first step that must continue as conditions change. 

The long-term fixes also require work. Controlling the growth and spread of Asian clams is possible using methods pioneered at Lake Tahoe, but it is expensive and requires continued effort year after year. 

Working with the League to Save Lake Tahoe, we are making a start by looking at how beach cleanups to remove algae may help reduce the nutrients. TERC scientists will take the collected algae and analyze just how much nutrient is removed with every bagful. Determining the best way to remove the algae and finding innovative ways to use it (for example, as compost or soil amendment) is a next step. 

What you can do     

Share your algae sightings – Let us know where you see algae and how it is impacting you by using the “Algae Watch” survey on the Citizen Science Tahoe Web App at citizensciencetahoe.app. Your reports are vital to “ground truth” what we’re observing through aerial photography, and will help us quickly locate emerging hot spots.   

Report algae blooms – If you think you’ve discovered a harmful algal bloom on the California side of the lake, please report it here: bit.ly/report-a-bloom. For reports in Nevada, call 1-888-331-6337. 

Learn more – Learn much more about algae, what the UC Davis Tahoe Environmental Research Center is doing to study its impacts on Lake Tahoe, and how you can help at tahoe.ucdavis.edu/algae.

Dr. Geoffrey Schladow, professor of civil and environmental engineering, was appointed founding director of the UC Davis Tahoe Environmental Research Center in August, 2004.