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Frequently Asked Questions

Cyanobacteria (Harmful Algae) Blooms and Recreational Advisories

What are cyanobacteria (harmful algae)?

Cyanobacteria are not algae at all. They are primitive bacteria found naturally in fresh and salt water all over the world. They are a beneficial bacteria that helped to create and sustain our oxygen atmosphere. In Warm weather, nutrients and low water flow can help these bacteria multiply quickly into what we call a bloom. Sometimes these blooms can produce cyanotoxins that can be harmful to people and pets.

Why is it called cyanobacteria?

The word "cyan" means blue-green, which is an appropriate name since most blooms are blue-green or green in color.

Why are these cyanobacteria blooms a health concern?

Not all blooms are harmful, but some cyanobacteria can produce cyanotoxins that can cause serious illness or death in pets, livestock and wildlife. These toxins can also make people sick, and in sensitive individuals also cause a red, raised rash or skin, ear and eye irritation.

What toxins are found in these blooms?

The most common toxins in harmful algal blooms in Oregon are microcystins and cylindrospermopsin

How can I be exposed? 

Exposure occurs when you swallow water with cyanotoxins during recreational activity, or when using affected water for drinking or cooking. Cyanotoxins are not absorbed through the skin, however, a red, raised rash or irritation of the skin and eyes can develop after contact with a bloom.

What are the symptoms of exposure? 

If enough water is swallowed you may experience one or more symptoms that mimic food poisoning; headaches, cramps, diarrhea, nausea and vomiting, numbness, dizziness, fever. Children and pets are at increased risk of exposure because of their size and level of activity. Symptoms generally begin within 24 hours and last 72 hours. .

When should I seek advice from a health provider or veterinarian? 

If you have severe diarrhea, vomiting, skin irritation or other related symptoms, or you experience these symptoms for more than 72 hours, you should seek medical attention to prevent severe dehydration or other problems. People with ongoing liver or kidney conditions should seek medical evaluation if they think their condition is worsening. Although it may be difficult to know if symptoms are related to cyanotoxin exposure, persistent symptoms should not be ignored. 
Dogs will exhibit symptoms after the first hour of exposure. Because dogs are susceptible to these toxins at extremely low levels it is very important to get your pet to a veterinarian as soon as possible if they show signs of diarrhea, vomiting, breathing problems, difficulty walking or standing or loss of appetite.

Are there treatments available if someone gets sick from a cyanotoxin exposure?

There are no antidotes for cyanotoxins. Health care providers can ease some symptoms to make you more comfortable. If you experience prolonged symptoms, drink plenty of fluids to help avoid dehydration. When seeking medical attention, let your health care provider know that you may have been exposed to cyanotoxins from a bloom. 

What does a bloom look like?

A bloom’s appearance can change over the course of its life, and different types of cyanobacteria can begin to grow once an initial bloom begins to die. Therefore, it is very important to continue visually monitoring a bloom. There are two major groups of cyanobacteria blooms. One can look foamy, scummy or thick like paint and is often blue-green, brownish red, pea green or white in color. The other looks like a dark green or black slimy mat that can have a smelly, offensive odor. Sometimes cells can be suspended in the water column, making it look bright green without a layer of visible scum. As blooms begin to die, they can disperse in the water. OHA’s website has photographs of different types of blooms based on the type of cyanobacteria involved.

When are recreational use health advisories issued?

A health advisory is issued when sampling data determines that cyanotoxin levels are above Oregon Health Authority recreational use values (RUVs). OHA has established RUVs for people and dogs, but advisories are only issued when levels are over the values for people. You should know that even if an advisory is not in place on a water body, a bloom and toxins can still be present, and in most cases harmful to your pet. Dogs are extremely susceptible at very low levels and exposure could result in death. If your pet exhibits any unusual symptoms after being in a water body you should seek advice from a veterinarian as soon as possible.

How will I know if a bloom is toxic?

Unfortunately, you can't tell if a bloom is producing toxins just by looking at it. Nor is the size of the bloom associated with the amount of toxins a bloom may be producing. Because we don't know why or when cyanobacteria produce toxins, it's impossible to predict when toxins are present unless sampling and testing is done.

How can I protect myself when camping or recreating at a lake with a bloom?

Stay out of water in or around a bloom and keep children and pets away. Never drink or cook with affected water, and do not allow your pet to drink water from the area. Although toxins are not absorbed through the skin, if you or your pet come in contact with a bloom, wash your skin or your pet thoroughly with another source of water and soap if available.

What precautions should I take when using power boats where a recreational use advisory is in place?

Although inhalation from boat spray is an exposure route, it is a low-risk exposure compared to ingestion (swallowing or drinking). That said, high-speed water activities such as water skiing, wake-boarding or power-boating should be avoided in areas where recreational advisories are in place, as these activities can increase incidental ingestion through falling and can aerosolize the water, making it easier to be inhaled. 

What about exposure at recreational facilities, like campgrounds and resident camps?

If drinking water comes from a public water system, campgrounds and residential camps will be notified of any do not drink orders when an issue develops and should follow the precautions advised. Check the system’s website for information. Many campsites are on domestic wells which are not usually impacted when a bloom is present. Direct any questions to the campground host or the agency responsible for the campground. If drinking water is pulled from the water body through a private intake and treated on-site, there could be issues. Check with the host or the responsible agency. An alternative source of water may need to be used unless the system has been tested to ensure reduction or removal of the specific cyanotoxin present. Boiling and camp-style filters are not effective at removing cyanotoxins. In fact, boiling will split cells open, releasing any toxins present. Tap water may be safely used for cleaning surfaces in facilities. Follow any public health advisory for recreational waters if issued by the Oregon Health Authority. Information on recreational water advisories can be found online on our Recreational Advisories page.

Can I eat fish or shellfish I catch in a water body under a recreational use advisory due to cyanotoxins?

Fish caught in affected waters pose unknown health risks. If you choose to eat them, remove all fat, skin and organs before cooking because toxins are more likely to collect in these tissues. Crayfish (crawdad) muscle can be eaten but discard all organs and liquids before preparing. It is illegal to harvest clams or mussels from freshwater lakes and you can be fined by the Oregon State Police if caught.

Can I treat toxins in the water to make it safe to drink?

Personal water filtration devices for camping or hiking have not been proven to be effective. Boiling water does not remove toxins and in fact, can increase toxins through evaporation. Most home filtration and treatment devices used to purify water drawn through private intakes are not capable of reducing or removing c cyanotoxins. However, for microcystin the global public health organization - NSF International has developed a microcystin test method for drinking water treatment units (NSF protocol 477). the method can verify a water filter's ability to reduce microcystin to below the health advisory levels for drinking water set by the EPA. Certified systems for the reduction of microcystin can be found here. If you do not own one of the certified systems, or there are other cyanotoxins present, the only way to know if an in-home treatment system is effective at removing or reducing these toxins is to have your drinking water tested when a bloom is identified near your intake.

What causes cyanobacteria blooms?

 It's difficult to know the specific cause of any one individual bloom. However, in general, sunlight, warm water temperatures, still water, and high nutrient (nitrogen and phosphorus) concentrations favor the development of these blooms. Nutrients can be naturally occurring (from wildlife and decaying vegetation) or arise from human inputs (fertilizer runoff, manure, failing septic systems, or forest management activities). While cyanobacteria blooms have been occurring since early in earth’s history, global climate change is likely to increase factors that promote cyanobacteria growth, increasing the frequency and duration of these blooms.  

How big can blooms get, and where are they most prevalent?

Cyanobacteria blooms change rapidly over the course of days and weeks. It is therefore difficult to characterize the size of the bloom in terms of acreage covered or volume of water affected. Not all areas of a lake or other water body may be equally affected. Blooms are often most concentrated around the water’s edge, and in coves, backwater areas, and arms of lakes and reservoirs.

Can any chemicals be used to get rid of a bloom?

Unfortunately, many mitigation methods that can be effective against cyanobacteria growth would harm the river or lake’s beneficial aquatic plant and animal life. These blooms naturally dissipate when conditions no longer favor their growth, such as cooler water temperatures, higher water flow, low sunlight and lower nutrient (nitrogen and phosphorus) concentrations. People can help to reduce teh development of blooms by using good management practices around water bodies. 

Why do blooms seem to appear overnight?

Most cyanobacteria have evolved to be able to control their buoyancy. By being able to sink and rise they can move to where nutrient and light levels are best. At night when there is no sunlight for cells to make food through photosynthesis, cells lose their buoyancy causing them to float to the water surface forming a scum which is seen the next day. During the day they can again move within the water column and are often moved around by wind and waves.

Who does the sampling, testing and reporting of results for recreational water bodies?

There is no statewide monitoring system. In Oregon, monitoring for cyanobacteria blooms and cyanotoxins on recreational waters is done on a voluntary basis by whichever agency or organization manages the water body. Monitoring for recreational purposes is not required by law or rule, and water body managers and organizations decide whether to test and when to test. OHA’s recreational sampling and advisory guidance documents provide information on best practices for water body managers. 

How often is sampling performed to determine whether an advisory is lifted or stays in place?

This is usually decided by water body managers for individual water bodies. OHA guidance recommends that sampling and analysis for cyanotoxins be conducted every other week after a bloom has been identified. However, OHA’s role is not regulatory, which means we cannot require water body managers to sample and analyze waters used for recreation. That said, if an advisory is issued based on data submitted to OHA, the water body manager must provide data to lift the advisory once the bloom is gone.

How many water bodies does OHA monitor?

OHA does not monitor any water bodies for cyanobacteria or cyanotoxins. Monitoring and sampling is at the discretion of the designated management agency. Such agencies include, but are not limited to, U.S. Army Corps of Engineers, U.S. Forest Service, Oregon Parks and Recreation Department, cities and counties. In general, these agencies have little to no dedicated financial and staff resources to carry out sampling and analysis throughout the season. Since OHA has no regulatory authority over monitoring, we can’t require agencies to monitor or sample for cyanobacteria or cyanotoxins, even when it is highly recommended.

Does OHA post recreational water quality results?

The public can access recreational data that triggers a recreational use advisory on the cyanobacteria (harmful algae) bloom website here: OHA does not post data below the recreational health advisory levels on the website.

Why are trigger levels for recreation and drinking water advisories different?

Recreational use advisories are based on concentrations of cyanotoxins measured in a water body—a reservoir, lake, or river. Drinking water advisories are based on concentrations of cyanotoxins measured in the finished water after treatment. Cyanotoxin concentrations are typically much higher on the water body than in finished water. Further, the amount of water people incidentally swallow while swimming, water skiing, etc. is much lower than when people use it as a primary drinking water source.

Are these blooms a new problem?

No. cyanobacteria are one of the earliest forms of life on earth and the toxic effects on livestock have been documented for more than 100 years. Bloom formation is linked to environmental conditions and nutrients which provide the elements necessary for cyanobacteria to multiply into what we call a bloom. Blooms are not going away any time soon as global climate change is increasing their frequency and duration through increased temperatures and sunlight, lower snowpack and decreasing water levels creating warmer water temperatures.

Is OHA investigating specific sources that cause cyanobacteria blooms?

OHA’s role is to advise the public on how to reduce exposures once a bloom has been identified. Natural resource agencies are better suited to investigate the causes of blooms, and to work on actions that may reduce the frequency of conditions that favor the growth of blooms.

Recreational Advisory Levels

Health advisory values are different for recreational and drinking water. 

The difference between the two reflects the amount of water children and adults incidentally ingest while swimming, water skiing, etc., and the amount of water ingested when drinking from the tap. 

Since much more water is ingested through drinking water, the health advisory values for drinking water are much lower than for recreational use advisories.

Recreational Use Values (RUVs) for Cyanotoxins in Recreational Water (in μg/L)

  • Microcystin: 8
  • Cylindrospermopsin: 15
  • Anatoxin-a: 15
  • Saxitoxin: 8

Recreational Water

The recreational use advisory values are based on incidental ingestion of water while people are recreating in water bodies affected by a cyanobacteria bloom and the cyanotoxins that may be produced. 

Since people are not intentionally drinking water while swimming, water skiing, wake-boarding or during other recreational activities, the amount of water incidentally ingested over time is much smaller than the amount ingested by children and adults when drinking tap water. 

For this reason, OHA uses the recreational values when determining exposures for children and adults while showering, washing hands, cleaning countertops, washing/rinsing teething rings, and all other activities that could result in incidental ingestion.

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