Being prepared for toxic algae season

As climate conditions continue to shift, Colorado has seen increasingly warm and nutrient-rich waters during the summer months — conditions that remain ideal for toxic algae to form in standing or slow-moving water. Toxic algae or harmful algae blooms (HABs) are made up of cyanobacteria, commonly known as blue-green algae. Although these organisms naturally occur in Colorado waters, they become a problem when they multiply rapidly, resulting in a dense cyanobacteria concentration or “bloom.” In drinking water sources, cyanobacteria blooms can cause the water to taste or smell bad. Taste and odor in drinking water is not regulated but creates customer concerns about water quality and safety. Most complaints that water utilities receive are about taste and odor, and these issues can last for prolonged periods. In addition to taste and odor problems, the blooms can become harmful and create a public health risk when they produce toxins. Removing toxins in a safe and cost-effective way can be a challenge for treatment facilities, and not all water providers are equipped to do so. 

Drinking water providers can contact the Water Quality Control Division at 303-692-3500 with questions about toxic algae. We can help water providers who experience taste and odor problems and toxins. This includes ideas about customer communication and steps that utilities can take to monitor and manage toxic algae and best treat their drinking water. If you detect microcystins above 0.3 μg/L and/or cylindrospermopsin above 0.7 μg/L (EPA’s cyanotoxin health advisory values), call the CDPHE 24-hour incident reporting hotline at 1-877-518-5608 so the division can provide you with immediate assistance.

We have resources to help drinking water providers and recreational water managers with toxic algae monitoring, response and public education and created a map to show recent toxic algae conditions for select waterbodies in the state. 

This 2019 AquaTalk article remains especially relevant today as cyanotoxins still pose a public health concern, even without being formally regulated. While EPA is continuing to evaluate the need for national regulation, the core takeaways from past events like Salem, Oregon’s microcystin advisory remain vital reminders for proactive communication, monitoring, and response. Whether you manage a public drinking water system or recreate on Colorado lakes and reservoirs, this piece offers timeless lessons for navigating toxic algae season safely.