Dear Lady of the Lake,
The lake is always green and there is so much algae, it’s everywhere. We are visiting another lake this weekend, will there be algae there too? How do we find out?
— Asking about algae
Dear Asking,
Thank you for asking this question, it’s timely and very important! There is also a lot of confusion around “algae” and what is commonly mistaken for algae. What you are probably concerned about is actually cyanobacteria. However, what you are noticing about your lake happens every summer, and not just in Clear Lake, but in other places around the state, around the Country, and around the world.
Now it’s important to recognize that algae is not cyanobacteria, and cyanobacteria is not algae. They may look similar to us standing on the beach or a boat, but they actually originate in different biological kingdoms. Cyanobacteria are as different to green algae as a mushroom is to a horse — they are not similar at all! They just happen to inhabit the same space — water.
Cyanobacteria belong in the Bacteria/Monera kingdom and green algae, or phytoplankton, belong in the protozoa kingdom.
For more information on the biological kingdoms and why algae and cyanobacteria are separated into different kingdoms, I recommend the Wikipedia page on Kingdoms. This page really does a good job discussing what is classified in each kingdom and some of the history of classification.
Before we go on, let’s review a few things.
Clear Lake is full of life, so it’s important for us to understand all that lives in the lake for us to understand what we are concerned about and what potential solutions are, and what their impacts might be on all things in the lake.
One: aquatic plants (or macrophytes) grow in the water, some are rooted in the lake sediments at the bottom and some are not rooted, and are free-floating.
Two: Green algae are microscopic plants (sometimes called phytoplankton) that are the primary fish food in the lake. Clear Lake is very green - that is from the green algae and that is why we have a world class fishery and people come from all over to catch record-sized fish living in the lake. The phytoplankton, or green algae is why Clear Lake is called “A Living Lake” as the productive green algae can sustain abundant life. In contrast, Lake Tahoe does not produce that much green algae because it is cold and dark, and does not have a work class fishery or as much life as Clear Lake.
For more information on Algae in Clear Lake, visit the “County of Lake Algae in Clear Lake” webpage.
Three: Cyanobacteria, which are sometimes called blue-green algae, are not really algae, but bacteria that live in the water alongside green algae. Cyanobacteria is also the culprit behind the “Harmful Algal Blooms, or HABs” colloquial. Cyanobacteria is NOT a preferred food source for fish. Sometimes when cyanobacteria populations grow in great numbers (called blooms) they can produce toxins that can cause public health hazards (hence their reference as Harmful Algal Blooms or HABs).
For more information about cyanobacteria, visit the “County of Lake Cyanobacteria” webpage.
So when someone states that they want to get rid of all the algae, that is usually not what they mean. The green algae is really, really important for our lake’s food web. It's the base of the food web and if it was all removed, we would see the collapse of the entire food web. From fish, otters, to birds, to all the living things that depend on green algae feeding fish. We would also see the elimination of our world class fishery.
Macrophytes, algae, and cyanobacteria all conduct photosynthesis, meaning they turn sunlight energy and carbon in the air into both oxygen and food energy or starch to grow. For macrophytes, algae, and cyanobacteria, the three main nutrients they rely on for growth are carbon, nitrogen and phosphorus.
Carbon and nitrogen are very abundant in the atmosphere and water, carbon in the form of CO2 and nitrogen in the form of N2 (gas) and any animal or plant waste or breakdown product in the water.
Phosphorus is least common, therefore phosphorus is the main driver of growth, because it’s normally least available, so it’s what limits growth of macrophytes, algae, and cyanobacteria. It’s not surprising that in Clear Lake, there is abundant light, warm temperature, and plentiful food nutrients. When the lake has excess phosphorus, we get excess growth of plants, algae, and cyanobacteria.
For more detailed information about Cyanobacteria in Clear Lake, refer to my first Lake of the Lake column from July 11,2021, “Concerned about Cyanobacteria in Soda Bay.”
For Clear Lake, there is a comprehensive cyanobacteria monitoring program managed by Big Valley EPA and other tribal partners. They have a website with most recent monitoring data posted. They sample about 20 sites every two weeks in the summer and every month in the winter. Results are also posted on the Facebook page called “Clear Lake Water Quality”. Red pins mean DANGER levels have been found and it’s recommended to not go into the water in that area. Orange pins mean WARNING, and yellow mean CAUTION. Green pins mean no cyanobacteria toxins have been detected in the sampled water from that area.
Cyanobacteria is not just a Clear Lake problem
As conditions around the country and the world change, cyanobacteria blooms are becoming more prevalent. Monitoring and reporting is also more widespread across the state and country. For example, here in California HABS data can be reported and shared on the My Water Quality HABS portal as part of the California Water Quality Monitoring Council.
On the California HABs portal is a link to a HAB Incident Reports Map, which provides data on voluntarily reported blooms in California. The data may include reports under investigation and/or confirmed incidents of HABs, but it’s a good visual to see what conditions are in water bodies in different parts of the state.
This site also provides a satellite freshwater HABmap <https://fhab.sfei.org/> tool developed by San Francisco Estuary Institute (SFEI). This map displays estimated amounts of cyanobacteria in large water bodies calculated from satellite imagery. The map includes approximately 250 water bodies in California large enough to be detected by the satellite. It is designed as a screening level analysis tool to indicate past 10-day aggregate conditions.
By exploring these tools, it becomes evident, and quite obvious, that cyanobacteria issues extend beyond Clear Lake, and are now becoming more frequent in other water bodies throughout the state.
The use of these tools in making informed decisions when recreating on or in freshwater is invaluable. Before planning a water excursion, you can see what current bloom conditions are in a lake of interest, and can use that knowledge to stay safe while enjoying the lake.
Cyanobacteria and HABS beyond California
Just this summer around the country, for example, there have been numerous reports of lakes or beaches closing due to harmful blooms. Here are a few examples from states like Colorado, New York, Michigan and Nebraska. This summer, lake monitoring revealed harmful cyanobacteria bloom conditions across the Country, further demonstrating that cyanobacteria is a serious issue that extends beyond Clear Lake and requires both state and national focus and attention.
Here are few:
A drinking water reservoir in Colorado was closed due to cyanobacteria bloom in August.
Ulster waterways had to issue warnings to the public after cyanobacteria bloom occurred.
In Michigan, throughout July and August, numerous lakes were reported and confirmed to have cyanobacteria blooms.
And as recently in September, in Nebraska, five lakes were under a health alert after testing confirmed cyanobacteria abundance above health triggers.
Therefore, it's important to be aware of conditions when visiting any freshwater water body, whether it’s located close to you or miles from home. Much like when you visit the ocean, you look for signs warning of rip currents, tides, or dangerous marine wildlife. When visiting freshwaters, keep aware of any posted signage.
Cyanobacteria blooms don’t always impact entire lakes or streams, and there can be areas that are less concerning, however you might have to spend a little time doing some research to find the monitoring data online from a local or state source. Every year more and more states are conducting monitoring and providing public health information so everyone can stay safe while enjoying their favorite lake, near or far.
— Sincerely Lady of the Lake
The CDC is a great resource for learning more about potential health impacts of cyanobacteria, what to look for, and how to protect you, your kids, and pets, when recreating in freshwaters.
Angela De Palma-Dow is a limnologist (limnology = study of fresh inland waters) who lives and works in Lake County. Born in Northern California, she has a Master of Science from Michigan State University. She is a Certified Lake Manager from the North American Lake Management Society, or NALMS, and she is the current president/chair of the California chapter of the Society for Freshwater Science. She can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..
Lady of the Lake: About algae
- Angela De Palma-Dow