Whatcom County health officials are warning residents to avoid contact with algae at Toad Lake after recent testing found microcystins, a toxin produced by blue-green algae, at levels that exceed recreational safety guidelines set by both the U.S. Environmental Protection Agency and the Washington State Department of Health. The lake is located approximately five miles northeast of Bellingham and draws swimmers, paddlers, and pet owners throughout the summer months, particularly during hot spells when lakeside recreation peaks.
What Was Found and Why It Is Dangerous
Microcystins are natural toxins produced by certain types of cyanobacteria, commonly called blue-green algae, when they bloom in warm, nutrient-rich water. The toxins were detected specifically in floating algae mats at the surface of Toad Lake. These mats form at the bottom of the lake, where they attach to submerged rocks, sand, mud, or aquatic plants. When conditions are right, including changes in water temperature, light levels, or wave action, the mats can break free from the bottom and rise to the water surface, where they concentrate along shorelines and in calm coves.
One of the most complicating factors with these blooms is visibility. The surrounding water can remain clear and appear perfectly safe even when algae mats are present nearby, making them hard to spot until they wash up on or near shore. The mats themselves can look like dark green, brown, or slimy carpet-like material floating on the surface. Children playing near the water's edge may not recognize the material as a hazard and could handle it thinking it is an interesting natural object.
Microcystin is a hepatotoxin, meaning it primarily attacks the liver. Exposure through ingestion, meaning swallowing water or algae, can cause abdominal pain, nausea, vomiting, headache, diarrhea, sore throat, blistering around the mouth, and in serious cases pneumonia. Skin contact with the mats can also cause irritation and rashes. The severity of symptoms depends on the dose and the size and health status of the person or animal exposed, which is why children and small pets are considered especially vulnerable. The U.S. Environmental Protection Agency has established recreational water guidelines specifically because of these documented health risks, and Washington State's Department of Health follows those benchmarks in issuing public advisories.
Guidance for Visitors, Children, and Pets
Whatcom County Health and Community Services is urging anyone visiting Toad Lake to take the following precautions until further notice. Avoid touching, eating, or swallowing any algae, and steer clear of areas where algae blooms or algae mats are visible on the surface or along the shoreline. Even brief skin contact with mat material can cause irritation, and any hand-to-mouth transfer of residue after touching algae is a meaningful exposure risk.
Do not let children play with or handle algae mat material. Young children are particularly at risk because they are more likely to put their hands in their mouths, more likely to accidentally swallow lake water while swimming, and more vulnerable to toxin effects because of their lower body weight. Even a small ingested dose can be enough to cause symptoms in a toddler or small child.
Pet owners should keep dogs and other animals away from any water with visible algae, and away from algae clumps on the shore. Dogs are particularly at risk because they are more likely to drink from the lake, lick algae off their fur, or roll in mat material on the beach. If your animal does come into contact with algae, rinse them off immediately with clean water and make sure they cannot lick their fur before you have fully cleaned them. Microcystin poisoning in dogs can be rapid and severe, with symptoms including weakness, vomiting, collapse, and in serious cases organ failure. If you suspect your pet has ingested algae and they show signs of illness, contact a veterinarian promptly rather than waiting to see if symptoms resolve on their own.
What Causes These Blooms and What Residents Can Do
Algae blooms are naturally occurring phenomena but their intensity and frequency are strongly influenced by human and animal activity in the watershed surrounding a lake. Nutrients from fertilizer applied to lawns and gardens, pet waste left near the shoreline, agricultural runoff from nearby fields, and wildlife waste all feed algae growth by increasing nitrogen and phosphorus levels in the water. Those nutrients act as fertilizer for cyanobacteria, allowing populations to build faster and reach toxic concentrations more readily than they would in a pristine watershed.
Warmer water temperatures also play a significant role, both by extending the growing season for cyanobacteria and by reducing the mixing of the water column that might otherwise dilute blooms. In a dry summer like 2026, when lake levels can drop and water temperatures rise due to reduced inflows and prolonged sun exposure, conditions for bloom formation are often more favorable than in cooler, wetter years. Toad Lake, like many smaller lakes in the region, may be particularly susceptible because of its shallower depth and the density of residential and recreational activity along its shoreline.
Whatcom County has seen periodic algae advisories at various lakes and water bodies over the years, and Toad Lake has faced similar conditions in prior summers. The county's Surface Water Advisories program monitors area lakes and issues public alerts when testing reveals toxin levels above recreational thresholds. For current and ongoing advisory status, residents can check the Whatcom County Health and Community Services page or visit nwtoxicalgae.org, a regional resource for harmful algae bloom information across the Pacific Northwest maintained by public health agencies in Washington and Oregon.
There is no timeline yet for when the Toad Lake advisory will be lifted. The county will conduct follow-up testing and will announce when toxin levels return to safe levels. Until that announcement is made, the guidance is to treat any algae mat you see at the lake as a hazard and keep children and pets well away from the water's edge in affected areas. If you visit the lake and notice unusual algae growth that has not yet been flagged, reporting it to Whatcom County Health is a useful contribution to the monitoring effort. For more information on water safety and outdoor recreation in Whatcom County, recent outdoor safety reporting covers the range of conditions that warrant caution this time of year.
