Algal Toxins/Cyanotoxins FAQ | Santa Clara Valley Water
Your Water
Ensuring safe, reliable water
Image
Your Water
Page Title
Your Water
Back to top

Algal Toxins/Cyanotoxins FAQ

Content

1. WHAT ARE HARMFUL ALGAL BLOOMS AND CYANOTOXINS?

Cyanobacteria, or blue-green algae, are found naturally in lakes, rivers, ponds, and other surface waters.  Under certain conditions, such as in warm water containing an abundance of nutrients, they can rapidly form harmful algal blooms (HABs). HABs may have negative impacts on ecosystems, and human and animal health. Some HABs are capable of producing toxins, called algal toxins or cyanotoxins, which can be harmful to humans and animals. [1]

 

2. HOW CAN HUMANS AND PETS BE EXPOSED TO CYANOTOXINS?

Human exposure to cyanotoxins generally occurs through ingestion or skin contact during recreational water activities (e.g. swimming and wading) when cyanotoxins are present, or by consuming drinking water or food (e.g. fish and shellfish) containing cyanotoxins. [2][3] 

Pets may be exposed to cyanotoxins if they drink water that has cyanotoxins, lick their fur after swimming in contaminated water with cyanotoxins, or eat algal scum or mats containing cyanotoxins. [2]

 

3. WHAT ARE POTENTIAL HEALTH EFFECTS FROM CYANOTOXINS TO HUMANS AND PETS?

In humans, potential health effects include upset stomach, fever, headaches, muscle and joint pain, vomiting and diarrhea, liver and kidney damage, and skin and eye irritation. [1][2][3]  

In pets, health effects from cyanotoxins may include skin rashes, vomiting, diarrhea, seizures, and even death. [2]  

 

4. ARE THERE DRINKING WATER STANDARDS FOR CYANOTOXINS?

Currently, there are no drinking water regulations for cyanotoxins. However, in 2015, the U.S. Environmental Protection Agency (EPA) issued 10-Day Health Advisories for the cyanotoxins microcystins and cylindrospermopsin (see Table below). Per the U.S. EPA, consuming drinking water that has cyanotoxins at or below the advisory levels for 10 days or less is not expected to cause adverse health effect to humans. 

 

EPA 100-day health advisories

5. ARE THERE REGULATIONS FOR CYANOTOXINS IN RECREATIONAL WATERS?

Currently, there are no state or federal regulations for cyanotoxins in recreational waters. However, there are U.S. EPA Health Advisories which are summarized in Table below. [4]

EPA health advisories for recreational waters

6. HAVE CYANOTOXINS EVER BEEN DETECTED IN VALLEY WATER’S TREATED DRINKING WATER?

Valley Water has a comprehensive algal toxin monitoring and response program. We routinely monitor cyanotoxins in Valley Water’s drinking water delivered from our three surface water treatment plants.  Since initiating the cyanotoxins monitoring program in 2015, there have been no detection of cyanotoxins in Valley Water’s treated drinking water.

 

7. HAVE CYANOTOXINS EVER BEEN DETECTED IN THE SOURCE WATER SUPPLYING VALLEY WATER’S TREATMENT PLANTS?

Cyanotoxins are detected routinely in reservoirs, mainly near the shoreline or boat launch areas. Drinking water source intakes are typically located in the deepest part of the reservoirs, well below the surface and far from the shoreline. As a result, very low levels of cyanotoxins have occasionally been detected in the source water supplying Valley Water’s treatment plants. At these plants, the water is treated to meet State and Federal drinking water standards before it is delivered to local water retailers. Cyanotoxins have never been detected in the water delivered by Valley Water. 

 

8. WHAT WILL VALLEY WATER DO IF IT FINDS CYANOTOXINS IN ITS TREATED DRINKING WATER?

If cyanotoxins were detected in treated drinking water, Valley Water would immediately notify the state regulatory agency for drinking water (State Water Resources Control Board’s Division of Drinking Water), the Santa Clara County Department of Environmental Health, and affected water retailers. Valley Water would also explore operational changes to reduce the level of cyanotoxins such as changing the water source supplying our water treatment plants or adjusting treatment processes.

 

9. DOES VALLEY WATER MONITOR CYANOTOXINS IN VALLEY WATER’S RESERVOIRS AND PONDS?

While recreational activities such as boating are allowed in some of Valley Water’s reservoirs, swimming and/or wading is prohibited in all Valley Water’s reservoirs and percolation ponds. This restriction applies to both people and pets. As such, Valley Water currently does not routinely monitor for cyanotoxins in its reservoirs and percolation ponds. Valley Water has a seasonal algae control program for percolation ponds that includes application of a harmless dye, an enzyme treatment, and/or algae harvesting. All recreational activities at Valley Water’s reservoirs are managed by the Santa Clara County Parks and Recreation Department [5], and the two agencies are working together on posting informational signage regarding algal blooms at Valley Water’s reservoirs.

 

10. WHERE CAN I FIND MORE INFORMATION ABOUT HARMFUL ALGAL BLOOMS AND CYANOTOXINS?

 

---------------------------------------------------------------------------------------------------------------------------------------

FOOTNOTES

[1] https://www.epa.gov/sites/production/files/2016-11/documents/harmful_algal_blooms_and_cyanotoxins_frequently_asked_questions.pdf

[2] https://www.epa.gov/sites/production/files/2016-12/documents/draft-hh-rec-ambient-water-swimming-factsheet.pdf

[3] https://www.epa.gov/sites/production/files/2015-07/documents/habs_faqs-and-resources_v1-july2015.pdf

[4] https://www.epa.gov/sites/production/files/2019-05/documents/hh-rec-criteria-habs-factsheet-2019.pdf

[5] https://www.sccgov.org/sites/parks