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Dear Lady of The Lake,
There is a weird smell coming from the lake at our lake house; it smells pretty bad. Is this something to be worried about? Was there a sewage spill?
Thanks,
From Worried about the Aroma, Eva.
Dear Eva,
Thank you for this question! I have actually gotten asked this several times recently. Anyone who has been outside anytime this week in the vicinity of the lake, might have also observed a specific odor associated with large, fresh waterbodies.
For a lake nerd, like me, I am not ashamed to say I love that smell. It means the lake is very alive and life is thriving. However, in some areas of the lake the smell can become very concentrated, and with a certain wind direction and temperature combination the smell can become singularly strong and sometimes noxious.
Lake signs of life and death
This time of year, when the sunlight days are long and the temperature is - finally! -warm, this is when growth in the lake is at its highest rates. This basically means that organisms from the smallest phytoplankton cell, to large clonal tule beds, to the largest catfish or river otter are growing the most this time of the year.
That’s because the conditions are the best for metabolic processes like photosynthesis and respiration, decompositions, nitrification, and denitrification. These are all very long words for saying that plants and animals, big and small, are happy, healthy and growing the most right now because it's easy for chemical processes to occur when it's warm. Also, the consumption and excretion processes are also in full force right now.
The smallest organisms in the lake, that mostly contribute to smells and odors, are green algae (phytoplankton) and blue-green algae (cyanobacteria). Cyanobacteria are not related to algaes at all, they are bacterias, but they look similar to our naked eye as green algae so historically they have been labeled an algae, and a blue-green algae for the colors they sometimes appear as.
Phytoplankton are simple microscopic organisms, like small plants. Cyanobacteria are aquatic bacteria, much smaller than phytoplankton, and they inhabit the same space as phytoplankton. Because both phytoplankton and cyanobacteria photosynthesize, they take in sunlight, carbon dioxide, and use nutrients from the lake as fuel, it’s easy to see why they are abundantly growing this time of year.
Cyanobacteria are usually single-cellular and can form colonies and dense mats at the surface of the water due to buoyant chambers some genera produce. The buoyancy characteristics of cyanobacteria means they can make themselves float at the surface of the water, usually in dense colonies, which can shade out the phytoplankton below them.
Sitting at the surface of the water, baking in the sun, can also cause death to some of the colony, causing a very strong odor in the near vicinity. After the cells die, they fall through the water column and break apart, releasing the nutrients they consumed as fuel, and neighboring cyanobacteria cells are now able to utilize those nutrients, grow, reproduce, and float to the surface of the water to conduct the whole cycle again.
This cycle of cyanobacteria, growing, reproducing, dying, and recycling for new cyanobacteria, is the most probable cause of the strongest odors coming from the lake right now and going into the end of summer and early fall.
Other sources of lake smells can be the decay of aquatic plants that have washed up along the shore and are rotting in the sun. Aquatic plants can also get tangled up with insects and baby fish, so those organic tissues can add to the decay and odors along the shorelines or in shallow, very warm areas of the lake.
Green algae that can also boom and busts cycles within the lake, with excess growth and decay giving off similar odors as dead plants. If you would like to learn more about green algae, or phytoplankton, you can visit the the County of Lake Water Resources Department “Algae in Clear Lake” webpage.
If you want more information on cyanobacteria, beyond that related to smells, you can visit my previous Lady of the Lake column from July 11, 2021, “Concerned about Cyanobacteria in Soda Bay."
What about spills,blooms, sheens, and foams
The likelihood of this smell being sourced to a sewage spill is very small, as sewage spills into the lake actually don’t have much of a strong smell because of the dilution of the lake water, and there is quite a bit of lake water (46,000 acres in fact!).
Secondly, there hasn’t been any reported spills the last few weeks at all, and for years there have not been any spills directly into the lake that were large enough to cause a persistent smell like you described.
You can learn about, search for, and find any reported hazardous spills at the CalOES Hazardous Spill Reporting Database. You can do a filtered search by county, and year, or a specific date.
Sometimes smells are accompanied by blooms, mats, sheens, or foams. Blooms can look like bright green, blue, purple, even reddish water, and mats can look like thick, almost solid, clumps, or layers on the surface of the water. Both blooms and mats can be attributed to specific genera of cyanobacteria.
Sometimes the water looks so opaque and blue green that people mistake it for paint spills. I actually responded to a report of spilled paint this year that turned out to be a cyanobacteria bloom – it’s not unusual and when you see it, it really does look like paint.
Sheens can appear when any natural decompositional process is occurring, such as the dying and decay of plants, animals, insects, or algae cells. Sheens are caused by oils that are released from the organisms during the decomposition process, and since oils are lighter in density than water, they will sit at the surface of the water and look much similar to an “oil spill” or “gasoline spill.”
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Rotting vegetation can also produce methane gasses, especially when it sinks to the muddy bottom of a lake or wetland. Microbes break down the decaying vegetation, which metabolically takes all the oxygen out of the system, and methane is a byproduct.
Methane can mostly just evaporate into the atmosphere, but when its concentrated in a small area, usually in a shoreline zone, trapped among some tules, or in a pool where water has receded, the methane molecules collect together, and appear as thick or rainbow sheens on the surface of the water. The hydrocarbons that make this methane phenomena are very similar in structure to the hydrocarbons in petroleum gasoline and oils used for engines, so that is why they are often confused with spills or illegal discharges.
Methane can become especially smelly when it is mixed with naturally occurring hydrogen sulfide, especially in environments that have high sulfates, which can include Lake County because there is high ambient sulfur background in the surrounding geology. This can mimic the smell of rotten eggs, and can be very obtrusive to some with acute senses of smell.
Need help identifying a bloom, mat, aquatic plants, or foam? Refer to this California Water Board HAB and Non-HAB visual guide.
Foams that accompany smells, or discolored water, are completely natural, although they get mistaken for pollution or discharge events. Foam is very natural for lakes and streams, and happens when there is an abundance of organic (i.e. carbon-based) materials in the water, which can break down surface tension of water making bubbles form. Physical lake processes, like wind or wave action, can concentrate bubbles into thick foams in a single area, or even a line parallel to a shoreline.
Sometimes the foams get mistaken for a “detergent spill” but detergents don’t last as long as natural foams since their sudsing agents are very short lived, and usually detergents have a pleasant, floral or perfume fragrance to them, which does not really correspond with reports of algae and lake smells.
Sometimes the foams occur out in the open water, and in combination with organismal processes, the lake appears to have lines or rows of green or brown or white foamy streaks. These are totally natural and way cool and called Langmuir Lines. You can learn all about these in my “Look, Look! It’s Langmuir Lines” column from March 2022.
Sometimes smells can arise from larger dead organisms, such as fish. Recent carp and goldfish die offs in the late, caused by a lab-determined koi herpes outbreak, is causing lots of large-bodies carp and goldfish to go belly-up and wash ashore near homes, parks, docks, and recreation areas on the lake.
Of course decaying tissue such as a fish would cause a particular strong odor, but will quickly dissipate naturally especially during windy and waving conditions. To speed up the process, should one be capable, a net and a trashcan will eliminate the odor completely. There is no public service that will collect and dispose of the dead carp in Clear Lake.
If you suspect there is a fish kill of a different species of fish, and in numbers that are unusual (more than a few) then you can report this to the California Department of Fish and Wildlife Mortality hotline, 916-358-2790, or submit a report to the online form.
For more information on Fish Kills, visit my column from August 2021 called “Figuring out Fish Kills.”
Much too smelly
I hope I answered your question Eva, and I wouldn’t worry about the aroma if I were you, it’s a sign that our lake is full of life.
However, if the smell becomes too strong, or noxious, and is impacting you, or someone in your family that has a history of respiratory problems, the State Of California Office of Environmental Health Hazard Assessment, or OEHHA, wants to know about it and has resources to respond. OEHHA can provide specialized guidance that is beyond the resources available at the local level.
To report a health impact from a bloom or cyanobacteria bloom, suspected bloom, from the lake, you can submit a report to OEHHA via the Harmful Algal Bloom Incident Reporting tool, called “Report a Bloom."
You can submit a report here online: https://mywaterquality.ca.gov/habs/do/bloomreport.html.
Or by calling their Report a Bloom hotline: 1-844-729-6466 (toll free).
It takes about a minute to fill it out, but it’s essential that the state receives this information so that they can respond and direct more adequate resources to cyanobacteria management and mitigation.
If you are interested in knowing where reports of blohttps://mywaterquality.ca.gov/habs/where/freshwater_events.htmloms are, so you can cross-reference with your location in help to identify a potential odor or condition in Clear Lake, or other lakes, you can visit the HAB Incident Reports Map.
In lakes, and other natural water bodies, like rivers, bogs, marshes, and wetlands, smells and odors are usually indicative of natural cycles of life and death. Aquatic ecosystems have a great way to effectively reusing and recycling materials, they just might get a little smelly along the way. Some odors can be pungent at times, but they are not permanent.
— Sincerely,
Lady of the Lake
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..