Harmful algal blooms

Swirls of bright green algae cover the surface of Lacamas Lake, with the gravel bank of the river in the background.

Harmful algal blooms occur when cyanobacteria grow out of control and produce toxins. These toxins, called cyanotoxins, can be harmful to people, especially children, and deadly for pets.

Not all algae and algal blooms produce toxins. But it’s impossible to know if a bloom is toxic just by looking at it. Laboratory testing is needed to determine if toxins are in the water. 

Several lakes in Clark County are prone to harmful algal blooms, including Vancouver, Round and Lacamas lakes. Educational signs are posted at these waterbodies. Public Health monitors blooms and issues advisories if toxin levels are higher than state recommendations. 

Benthic algae mats

Another type of harmful algae (or cyanobacteria), called benthic algae mats, was first found in Clark County waters in October 2024. Like algal blooms, benthic mats can also produce toxins that can make people and pets sick. 

Benthic algae mats were discovered in Clark County when a dog died after eating the algae along the shoreline of the Columbia River. Since then, benthic algae mats have been identified at several locations along the Columbia River. Signs are posted at these locations, encouraging people to check for algae before recreating in the water.

How to identify harmful algae

Be sure to check for cyanobacteria that can produce harmful toxins before getting into local lakes and rivers. The best way people can protect themselves, their children and their pets from this harmful algae is to avoid contact.

Algal blooms that can produce harmful toxins:

  • Are usually found in ponds, lakes and slow-moving water
  • Can look like foam or scum on the surface of the water
  • Can look like streaks of paint in the water
  • Can be green or blue but may also be red or brown
  • Can accumulate on the shore and look like clumps where foam or scum dried
  • Can make water less clear as the bloom gets more dense
Algae off of Leadbetter Rd
Blue-green colored algae covers the surface of the water at Round Lake. In the background is the dam at Round Lake.
A thick layer of algae scum lines the rocky shore at the Vancouver Lake flushing channel.


Benthic algae mats that can produce harmful toxins:

  • Can be found in fast-moving water, like rivers, and slow-moving water
  • Can be attached to the riverbed or lakebed on plants, rocks, sand or wood
  • Can detach from the bottom and float on the surface of the water or wash ashore
  • Can be in clumps, blobs, mats or spires
  • Can be bright and dark greens, yellow, brown, orange or red
  • Can be slimy, gelatinous or slippery
  • Does not affect the clarity of water 
Benthic algae mats in the water on top of rocks.
A benthic algae mat is attached to the riverbed beneath 5 inches of water in the Columbia River.
A clump of benthic algae mat material is stuck to rocks beneath the surface of the Columbia River.


Before visiting local waterbodies, check for advisories. And when in doubt, stay out. 

When in doubt, stay out - HABs EPA

 

Getting sick from harmful algae

Cyanobacteria can produce toxins that can make people and animals sick. Children and household pets are most likely to get very sick because of their smaller body sizes and higher likelihood of ingesting water.

People can be exposed to toxins in the water by:

  • Swallowing water while swimming or recreating
  • Breathing water droplets during water activities, like waterskiing or paddling
  • Having skin contact during swimming, boating or other water activities
  • Eating fish or shellfish from lakes or ponds with toxic algae

Pets can be exposed to toxins in the water by:

  • Drinking from lakes, ponds or other waterbodies with toxins
  • Licking their fur after swimming in water with toxins
  • Eating clumps of algae from shorelines or in shallow water

Cyanobacteria can also deplete oxygen in the water. This can suffocate fish and other aquatic organisms and cause fish die-offs.

Symptoms

The toxins from cyanobacteria can affect the liver and nervous system. The type and severity of symptoms vary. People and pets may begin having symptoms within minutes to a few hours after being exposed to toxins. 

People who have been exposed to toxins may experience:

  • Rash, itching, blisters, eye irritation
  • Abdominal pain, diarrhea, vomiting, nausea
  • Headache, sore throat, fever
  • Numbness of the lips, tingling in fingers and toes, dizziness 
  • Wheezing, coughing, chest tightness, shortness of breath, difficulty speaking

Pets who have been exposed to toxins may experience: 

  • Diarrhea, vomiting, not eating
  • Excessive drooling or foaming
  • Stumbling, loss of motor control, weakness, disorientation
  • Difficulty breathing 

Sudden death of pets may also occur.

People or pets that come into contact with water containing cyanobacteria should rinse off with clean, fresh water as soon as possible. People who experience symptoms should seek medical care right away. Pets that experience symptoms should be seen by an emergency veterinarian immediately.

Report algal blooms

Public Health relies on members of the community to report algae blooms. Submit reports of suspected algae blooms through our online portal. Please include photos of algae blooms with the reports.