Preparing for Harmful Algal Bloom Season

Water that is warm, slow moving and high in nutrients can cause harmful algal blooms to form in waters above ground like reservoirs. With the weather warming up, managing these waters to prevent these blooms becomes critical for water safety. Certain types of cyanobacteria, also known as blue green algae, produce unpleasant taste and odors in water. Some blue green algae are also capable of producing cyanotoxins which can create health risks for humans and animals. The toxins can be problematic for anyone that ingests them or is exposed through recreational activities. Currently, cyanobacteria is not a regulated contaminant but EPA has published non-regulatory drinking water 10-day health advisories for the cyanotoxins microcystin and cylindrospermopsin based on studies showing that these two strains cause liver, kidney and reproductive toxicity.

Responding to situations where an unregulated contaminant measures above a health advisory is very difficult because there is not a playbook with available instructions like there is with regulated contaminants. In May 2018, Oregon’s capital and second-largest city, Salem, made national headlines by declaring a state of emergency after issuing a “Do not drink” advisory due to elevated microcystin levels in their treated water. Here are a couple of the lessons learned Salem shared after the event:

Do not wait to notify your customers

After receiving initial sample results showing levels above the health advisory, the system spent a couple of days making operational changes to try and lower toxin levels before taking more samples. Because Oregon didn’t have any labs capable of cyanotoxin analysis, they had to ship samples to an out-of-state lab, causing a long turnaround time for receiving results. The system believed it was okay, since they were still responding within the 10-day health advisory window. However, those follow-up sample results came back high and the system issued a “Do-not drink” advisory. The customers and local papers were outraged because they weren’t notified sooner.

Knowing when to lift the advisory is tricky 

After receiving sample results showing microcystin levels were below the health advisory, the city lifted the initial “Do not drink” advisory. The city then issued another “Do not drink” advisory four-days later after receiving additional results showing elevated toxin levels. They waited to lift the second advisory until they had levels below the health advisory for 12 consecutive days.

Between 2018 and 2020, all drinking water systems nationwide serving over 10,000 individuals, as well as a random selection of other systems, are required to sample for cyanotoxins as part of EPA’s Unregulated Contaminant Monitoring Rule (UCMR). EPA will use the test results to see where cyanotoxins are occurring and determine whether or not to regulate them in the future. There are over 100 Colorado drinking water systems required to perform this additional testing and they have been notified. As of May 2019, there have not been detections of any UCMR cyanotoxins in treated water.

Online resources

Learn more about cyanotoxins and how to monitor and prepare for them by reviewing these resources:

• Monitoring guidance created by the Colorado Harmful Algal Bloom Workgroup.
• EPA's  toolkit and webinar Preparing for HABs season. 

➽ David Dani, Local assistance unit