Montana Department of Environmental Quality About Us Permitting & Operator Assistance Public Participation

Harmful Algal Blooms (HABs)

Program Overview

Nonpoint source pollution can cause harmful effects such as harmful algal blooms (HABs), which are an overgrowth of cyanobacteria. Some types of cyanobacteria can produce toxins that can pose serious health risks to humans and animals if toxins are contacted or ingested. HABs typically occur on lakes and reservoirs when water conditions (e.g., light, temperature, and nutrient levels) promote growth; typically, in summer and fall in Montana. If in doubt, stay out.

HABs Contacts

Water Quality Specialist
Hannah Riedl (406) 444-0549


Think you see a HAB?
Think you or an animal have been exposed to a HAB?
  • Talk to your health provider or veterinarian
  • Call poison control 1-800-222-1222
  • Call animal poison control 1-888-426-4435 (fee based)

Maps & Media

Harmful Algal Blooms - When in doubt stay out!
Harmful Algal Blooms - Webinar - 2022
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