Wyoming Officials Issue Cyanobacteria Bloom Warnings

State agencies urge residents to avoid waterways affected by harmful algal blooms across Wyoming.

Updated on Oct. 24, 2026 in Current Conditions

Slimy blue-green algal mats cling to the edge of a cold, stagnant lake with rocky shores in Wyoming. — Wyoming environmental and health officials have issued ongoing warnings regarding toxic cyanobacteria blooms affecting multiple state waterways this October. AI Illustration. Upload story photo >

Live Poll

Do you check for local water safety advisories before fishing or recreating in public waterways?

The Wyoming Department of Environmental Quality, Department of Health, and Livestock Board have issued warnings regarding cyanobacteria blooms present in state waters. As of mid-October, dozens of locations remain under bloom and toxin advisories.

Why it matters

Warmer air temperatures combined with below-normal snowpack and precipitation levels have led to lower, warmer water conditions that encourage bloom formation. These blooms can persist even through freezing temperatures, posing risks to public health and livestock.

As of October 15, 2026, 42 Wyoming waterways remain under active bloom advisories, with 10 of those locations specifically flagged for toxin presence. Blooms often appear as surface scum, clumps, or mats resembling spilled paint or grass clippings.

The players

Wyoming Department of Environmental Quality

This state agency is responsible for monitoring water quality and issuing public health advisories regarding harmful environmental conditions.

Wyoming Department of Health

This department works in conjunction with environmental regulators to assess and communicate health risks posed by contaminated public water sources.

Wyoming Livestock Board

This board monitors agricultural health risks and collaborates on warnings regarding water safety for livestock in the state.

The details

Cyanobacteria can create slimy or chunky mats on submerged surfaces that may detach and wash up along shorelines. Officials from multiple state departments are tracking these developments to manage safety risks for the public.

July 2026: The Department of Environmental Quality issued a health advisory for Lake DeSmet.
August 21, 2026: The health advisory for Lake DeSmet was officially lifted.
October 15, 2026: Forty-two state waterways were reported to have active bloom advisories.

Seasonal Patterns

The current uptick in advisories extends the water quality monitoring standards established under the Clean Water Act. These seasonal blooms are intensified by shifting precipitation levels, marking a departure from typical water quality baselines seen in higher-snowpack years.

Residents should avoid any waterways displaying material that looks like spilled paint, scum, or grass clippings, as these are indicators of potential blooms. Because blooms can survive freezing temperatures, recreational users should remain cautious even as seasonal temperatures drop.

The takeaway

Public safety relies on recognizing the visual signs of cyanobacteria, such as surface scum and mats. Staying updated on state-issued advisories helps prevent accidental exposure for people and livestock.