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Algal Bloom Info

Recognizing the growing concerns with harmful algal blooms (HABs), and in response to worsening conditions brought on by the current drought, U.S. EPA Region 9 has produced this list of frequently asked questions and resources on HABs and cyanobacterial toxins or “cyanotoxins.”

What are harmful algal blooms?
Algae are very important to both freshwater and marine environments and most species are harmless under normal circumstances. Cyanobacteria are commonly referred to as “algae” or “blue-green algae” but they are actually photosynthetic bacteria that share properties with algae. They are naturally found in fresh and marine aquatic water bodies and when present in large quantities as “blooms”, they can impact recreational, aesthetic, aquatic life and drinking water beneficial uses of waterbodies. Biomass from blooms can cause anoxia, hypoxia, and habitat alteration, and impact drinking water systems; and cyanobacteria can produce toxic compounds (cyanobacterial toxins or “cyanotoxins”) that can pose a significant potential threat to human and ecological health and affect taste, odor and safety of drinking water. These harmful cyanobacterial blooms, commonly referred to as “harmful algal blooms”(cyanoHABs) have the potential to cause adverse health effects in humans and animals through the degradation of waterways used for recreational purposes and as drinking water supplies.

What are the common causes of harmful algal blooms?
Under the right conditions cyanobacteria can multiply rapidly, forming a bloom in the water; sometimes a blue-green “scum” forms on the water surface, though blooms can be green, blue, red or brown. While not well understood, when conditions are favorable, cyanobacteria can produce cyanotoxins. Increased inputs of nutrients like nitrogen and phosphorous, often from human land use practices, promote cyanobacterial growth and can lead to increased occurrences of HABs. Low flows, stagnant water, increased intensity and duration of sunlight, and sustained high temperatures, as we’ve experienced with the current drought, create the ideal conditions for freshwater cyanoHABs and can lead to new, larger and prolonged blooms.

What are the possible effects of harmful algal blooms?
Human exposure to cyanobacteria and cyanotoxins generally occurs through recreational contact (ingestion, inhalation, dermal contact) and ingestion of drinking water. The acute effects of contact recreational exposure from activities like swimming, jet skiing, etc., can result in a wide range of symptoms in humans including skin and eye irritation, fever, headaches, muscle and joint pain, blisters, stomach cramps, diarrhea, vomiting, mouth ulcers and allergic reactions. Effects can occur within minutes to days after exposure. In severe cases, seizures, liver failure, respiratory arrest, and (rarely) death may occur. In the most recent survey by the Centers for Disease Control and Prevention (CDC), for the years 2009-2010, eleven freshwater HAB-associated outbreaks were reported by New York, Ohio and Washington and resulted in 61 known illnesses, 2 hospitalizations and no deaths.i The most common effects are observed in dogs and livestock due to consumption of water with cyanotoxins or grooming after swimming. In 2015 alone, several dog deaths have been linked to cyanoHAB exposure from California waters. Fish and aquatic animal and plant die-offs can also occur when blooms block sunlight or when they decay and oxygen in the water is depleted resulting in hypoxic conditions.

When located near drinking water intakes, HABs can result in taste and odor problems in treated drinking water. Management practices that water utilities already use to address taste, odor and operational effects of algae are generally effective at removing cyanobacteria and cyanotoxins but there is potential for drinking water to contain cyanotoxins if the proper treatment process is not used.

In estuaries and marine environments, both freshwater and marine cyanobacteria with associated toxins can accumulate in fish and shellfish that can, if gone undetected, be consumed by humans and result in poisoning.iii These cyanotoxins are also known to impact health and cause death in fish and marine mammals.

Economic losses can occur due to impacts on recreation, such as fishing, swimming and concessions, and increased costs to manage and treat drinking water supplies.

How can cyanotoxins be detected?
The presence of cyanotoxins cannot be determined simply by looking at a bloom. Detection of cyanotoxins requires collecting representative samples and analyzing for cyanobacteria and/or cyanotoxin levels. There are several monitoring methods designed for different types of cyanotoxins and with varying levels of accuracy, cost, availability and detection limits. The most common are commercially available field test kits that easily detect presence and absence and do not require expensive equipment or extensive training. More precise analytical methods are recommended as follow up when presence is detected.

How can you protect yourself from exposure to cyanotoxins?
The following recommendations are based on guidance from the State of California and should be followed to avoid recreational exposure to cyanotoxins:

  1. Avoid wading, swimming or jet or water skiing in water containing cyanobacteria blooms or scums or mats.
  2. Do not drink, cook or wash dishes with untreated surface water from these areas under any circumstances; common water purification techniques (e.g., camping filters, tablets and boiling) do not remove toxins. Even when blooms are not present, still carefully watch young children and warn them not to swallow the water.
  3. People should not eat mussels or other bivalves collected from impacted areas. Limit or avoid eating fish; if fish are consumed, remove guts and liver, and rinse filets in clean drinking water.
  4. Get medical treatment immediately if you think that you, your pet, or livestock might have been poisoned by cyanotoxins. Be sure to alert the medical professional to the possible contact with cyanobacteria.
  5. Take care that pets and livestock do not drink the water, swim through algae, scums or mats, or lick their fur after going in the water. Rinse pets in clean drinking water to remove algae from fur.

How can harmful algal blooms be treated and managed?
California issued health-based action levels or voluntary guidelines for recreational exposure to cyanotoxins. They include action levels for humans, pets and livestock under selected scenarios for microcystins, cylindrospermopsin, and anatoxin-a. California recommends public advisories for recreational exposure and additional monitoring at or above 0.8 microgram per liter for microcystins, 4 micrograms per liter for cylindrospermopsin, and 90 micrograms per liter for anatoxin-a. However, levels protective of pets and livestock differ and are in several cases lower than action levels for human exposure. Guidelines for health based action levels were also derived for concentrations in sport fish and shellfish.

Where are harmful algal blooms occurring in Region 9?
Based on previous years’ experience, EPA is aware of numerous water bodies in Region 9 where HABs are known to occur. EPA continues to learn of new and persistent HABs through working with federal, state and local partners and will continue to provide support to address this serious issue. Water bodies with recurrent HABs include Pinto Lake near Monterey; Lake Temescal, Lake Chabot and Del Valle Reservoir in the San Francisco Bay Area; San Francisco Bay Delta, including the North and South Bay Aqueducts; the San Joaquin River and Clifton Court Forebay near Stockton; Bethany Reservoir near Livermore; Clear Lake; Klamath River and Iron Gate and Copco reservoirs; Eel River; Trinity River; and the Colorado River, Lake Mead, Lake Powell, and Central Arizona Project.

Who should you contact with questions or concerns about HABs in Region 9?

County health department listings and contact information are available at the California Department of Public Health’s website.

Drinking Water
For questions and concerns related to drinking water exposure in California, contact the county health department, or contact the nearest State Water Resources Control Board Division of Drinking Water District Offices here.