Harmful Algal Blooms Warning Issued Statewide

HELENA — Montana Department of Environmental Quality (DEQ) and public health officials are sounding the alarm as toxic algal blooms continue to appear in lakes and reservoirs across the state. The harmful cyanobacteria, which produce dangerous toxins, have been detected in multiple popular recreation spots, raising concerns for swimmers, boaters, anglers, and pet owners during peak summer months.

Algal blooms thrive in warm, nutrient-rich waters — conditions that have become more common due to rising temperatures and occasional runoff from agriculture and development. DEQ monitors have reported elevated levels of microcystin and other toxins in several water bodies, including portions of Canyon Ferry Reservoir, Flathead Lake, and smaller lakes in the western and central parts of the state.

Health officials stress that not all algae are dangerous, but certain blue-green varieties can produce potent toxins that affect the liver, nervous system, and skin. Symptoms of exposure can range from rashes and eye irritation to vomiting, diarrhea, and in severe cases, more serious illness, particularly in children, the elderly, and pets.

"Montanans love their lakes, and we want everyone to enjoy them safely," said a DEQ spokesperson. "We strongly recommend checking our harmful algal bloom map before heading out and avoiding water that looks green, scummy, or has a strong odor."

The warning comes as families prepare for weekend outings and summer vacations. Officials advise keeping pets out of affected water, rinsing off after swimming, and never allowing animals to drink from suspicious sources. Boaters are encouraged to clean equipment thoroughly to prevent spreading blooms between water bodies.

While some blooms are naturally occurring, experts note that human activity — including fertilizer runoff and warming waters linked to climate trends — can worsen the problem. Montana's vast network of rivers, lakes, and reservoirs makes the state particularly vulnerable during hot, dry periods.

Local communities are responding with increased monitoring and public education. In areas like Bozeman and the Flathead, signage has been posted at popular access points, and some campgrounds are providing updated safety information.

For those planning outdoor activities, DEQ maintains an online map showing current bloom locations and risk levels. When in doubt, the safest approach is to avoid contact with discolored water and keep pets on leash near shorelines.

This is not the first year Montana has faced algal bloom challenges, but officials say the frequency and intensity appear to be increasing. State agencies are working with local governments, tribes, and conservation groups to study long-term solutions, including better nutrient management and watershed protection.

In the meantime, Montanans are urged to stay informed and prioritize safety. Enjoy the beauty of Montana's waters responsibly — because a single careless swim or drink from the wrong spot can have serious consequences.

For the latest updates, visit the Montana DEQ Harmful Algal Bloom webpage or contact your local health department.

Stay safe out there, Montana. The state's natural treasures are worth protecting — and enjoying with caution.