Harmful Algal Blooms in Lake Tahoe and the Tahoe Keys
What are Harmful Algal Blooms
Cyanobacteria are small microbes or bacteria that live in nearly every habitat on land and in the water. They have existed for billions of years as essential components of freshwater ecosystems and form the foundation of most aquatic food chains.
When these organisms produce dangerous toxins, they are commonly referred to as harmful algal blooms or HABs. Environmental conditions that favor the growth of HABs and algae include warm temperatures, low or stagnant water flows, and excessive nutrient inputs. When these conditions are present HABs can multiply rapidly creating nuisance blooms.
Some HABs can produce toxins that can harm pets, wildlife, or people. Not all HABs produce toxins, but those that do can cause a multitude of health issues and even death.
There are two types of HABs. The first type is known as planktonic (HAB suspended in the water column), and the second is known as benthic (HAB that grows attached to the bottom or other objects under the water's surface). For the purpose of this Story Map, the focus will be on Planktonic HABs and the corresponding signage.
In California, harmful algal blooms are most common during the warm weather months between late May through October, but they can occur all year.
Understanding Health Advisories Associated with HABs
The Water Board relies on four tiers of signage to inform the public about HABs. The HAB advisory signage serves to recommend actions to keep you, your family, and your pets safe when recreating near waterbodies that are experiencing a HAB. The signage is based on laboratory result trigger levels except for caution which can be recommended based on visual observations and/or laboratory results. Each advisory sign has different recommendations for protection of public health and exposure for recreation. Be sure to follow signage recommendations.
When are advisory signs posted?
Planktonic HAB advisory signs are voluntarily posted once laboratory results confirm the presence of HABs in the water column or if visual indicators (e.g discoloration, scum, soupy or paint like appearance) are observed following the voluntary guidelines for cyanobacteria in California recreational waters . A planktonic HAB advisory sign may also be posted in response to, and while investigating, a report of a potential HAB-related human or animal illness.
General Awareness Sign
If this is the only sign present at a waterbody there is currently no advisory at the location. This sign may stay up year-round at waterbodies because it provides the public with general information about HABs, potential symptoms, and general precautions.
Even if no advisory is present, you should always be aware of the visual appearance of a HAB (e.g discoloration, scum, soupy or paint like appearance) and stay away from it if you see one.
You can learn how to visually differentiate between non-toxic algae and aquatic plants compared to HABs by utilizing this short guide.
Caution Advisory
Caution is associated with the lowest advisory level. It can be put in place with visual confirmation of a potential HAB. It can also be put in place if laboratory results exceeding the caution toxin trigger level. Many Lake Tahoe beaches have these signs up during the season based on visual observation alone.
Warning Advisory
Warning is the middle advisory level. Posting of warning signage is advised when laboratory data confirms the presence of toxins exceeds specific trigger levels. Lake Tahoe has never reached an advisory of this level; however, in the past, various locations within the Tahoe Keys Lagoons have experienced toxin levels that prompted a warning advisory level.
Danger Advisory
Danger is the highest advisory level. Posting of danger signage is advised when laboratory data confirms the presence of toxins exceeds specific trigger levels. Lake Tahoe has never reached an advisory of this level; however, in the past, a few locations within the Tahoe Keys Lagoons experienced toxin levels that prompted a danger level advisory.
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Examples of algae seen around Lake Tahoe
The following map walks you through areas that have had harmful algal blooms or non-harmful algae. The text lets you know what advisory (if any) was present at the time the images were taken. On the right side of the images is an arrow to flip through other photos taken at a single location.
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Connolly Beach
Caution advisory based on visual observation.
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El Dorado Beach
Caution advisory based on visual observation and laboratory data.
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Regan Beach
Caution advisory based on visual observation and laboratory data.
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Barton Beach
Caution advisory based on visual observation and laboratory data.
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Cove East
Caution advisory based on visual observation.
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Pope Beach
Caution advisory based on visual observation.
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Jameson Beach
Caution advisory based on visual observation.
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Kiva Beach
Caution advisory based on visual observation and laboratory data.
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McKinney Bay
No advisory. Typical non-harmful alga that have been present in Tahoe for about 30 years. This algae typically appears around early spring. The algal material may be attached to the rocks, floating in the water column, or washed up on shore.
Even though this type of algae is typically not harmful, harmful algae has been known to integrate into many different environments so it still may not be safe to recreate in an area that appears like this.
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Kings Beach
Caution advisory based on visual observation.
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Examples of HABs seen around the Tahoe Keys Lagoons
The following takes you through images of what the water in the lagoons have looked like. The images are in order from least harmful to highest advisory. The advisory levels are indicated in the text. On the right side of the images is an arrow to flip through other photos taken at a single location.
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In between White Sands and Balboa Dr.
No advisory in either photo. You see aquatic weeds present.
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Lucerne Way and Venice Dr.
In the first photo there is no advisory. You see aquatic weeds and a small amount of non-harmful algae.
In the second photo there is a caution advisory. You see a paint like appearance on the water. The advisory was based on visual observations and laboratory results.
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In between Emerald and Kokanee Way
In the first photo there is no advisory. You see water that is not discolored.
In the second photo there is a caution advisory. You see water that is turning green. The advisory is based on lab results.
In the third photo there is a warning advisory. You see green water that has a paint like appearance of a HAB. The advisory is based on lab testing.
In the fourth photo there is a danger advisory. You see bright green water that has a paint like appearance of a HAB. The advisory is based on lab testing.
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Corner of Venice and Alpine Dr.
In the first photo there is no advisory. You can see no discoloration of the water.
In the second photo there is a danger advisory. You see a bright green paint like appearance of a HAB. The advisory is based on lab results.
Extra Resources:
For more in-depth information on the topics presented on this StoryMap visit the following websites:
HAB Advisory Explanations and Monitoring within Lake Tahoe and the Tahoe Keys
