On April 12, 2023 the Missouri Clean Water Commission (CWC) voted against proceeding with the rulemaking process to adopt the EPA’s 2019 recommendations for human health recreational criteria for two cyanotoxins produced by Harmful Algal Blooms (HABs). The Missouri Department of Natural Resources (DNR) recommended to the CWC that the rulemaking for the water quality criteria proceed to the public comment period process. This recommendation came after MCE petitioned DNR in November 2021 to adopt these criteria. DNR subsequently held stakeholder meetings as well as developed a Regulatory Impact Report for the proposed criteria. The CWC rejected DNR’s recommendation by a 5-1 vote.

What was the Proposed Rule?

DNR recommended to the CWC that 10 CSR 20-7.301 be amended by adopting water quality criteria for two cyanotoxins often produced by harmful algal blooms: microcystin and cylindrospermopsin. The toxic effects of microcystins primarily target the liver, among other impacts, while cylindrospermopsin targets both the liver and kidneys (link, pg. 59-71). Cyanotoxins like microcystins and cylindrospermopsin come from cyanobacteria, which are commonly referred to as blue/green algae. 

The proposed water quality criteria for human health recreation were 8 μg/L for microcystins and 15 μg/L for cylindrospermopsin. These criteria would have only applied to lakes greater than 10 acres, designated for recreational use, and qualify as Waters of the State (governed by Missouri). It would not have applied to smaller, privately owned lakes or reservoirs. If CWC had allowed DNR to proceed and 10 CSR 20-7.301 ultimately was amended after a public comment period, the water quality criteria would have matched those recommended by the EPA in 2019. MCE petitioned DNR to consider these criteria because of the threat that Harmful Algal Blooms can pose to the health of humans, animals, and the environment. 

What are Harmful Algal Blooms?

Algal blooms occur when a population of algae in a waterbody increases rapidly and results in detrimental impacts on other organisms. Algal blooms often occur when there is an excess of nutrients in the water from pollution which fuels growth. A bloom that negatively impacts people, animals, or the environment is referred to as a Harmful Algal Bloom (HABs).  The impacts of HABs can vary in type and severity. Sometimes the growth of the algae may use up the oxygen in the water, leaving less for the other aquatic organisms and potentially killing them. Sometimes the bloom may release toxins that are harmful to other organisms. HABs have been known to cause mass die-offs of aquatic organisms, colloquially known as “fish kills”, as well as pose a threat to humans, livestock, and pets.

What do Algal Blooms and HABs look like? 

Blooms of algae can take on multiple appearances, including “foam, scum, mats, or paint on the water”, as well as “change the color of the water to green, blue, brown, red or another color” (link). However, a bloom may still be occurring even if there are no visual indicators of its presence. If you see one in a nearby lake or stream, report it to DNR

HABs Nationwide and in Missouri

HABs occur across the nation. The Centers for Disease Control and Prevention (CDC) had hundreds of reports from 22 states of HAB events from 2016 to the end of 2020. However, not all occurrences of HABs are detected or reported to the CDC, so these numbers may be an underestimate. Additionally, the state and federal reporting structure for instances of HABs harming human health is currently limited. A sense of the issue’s scale is given by a 2017 report from the U.S. Geological Survey, which indicates that 43 states, including Missouri, had seen HABs implicated in human or animal illness or death.

While current monitoring efforts in Missouri make it difficult to fully confirm the presence of a HAB when a report is made, there has been an increase in the number of reported HABs. With DNR data collection beginning in 2010, 79% of the 197 HABs reported overall occurred within the last 5 years (link). This increasing trend in reports is also seen for the type of waterbody that the proposed criteria would have applied to, namely lakes that are (1) Waters of the State (2) greater than 10 acres, and (3) designated for allowing whole human body contact (link). Between 2017-2022, sampling efforts conducted by DNR, the Army Corp of Engineers, and partners found conditions that would have been considered exceedances of the proposed criteria at 5 locations in Missouri: Catclaw Lake, Drexel City Reservoir South, Pomme de Terre Lake, and Chaumiere Lake (link, link).


HABs pose a threat to human health and Missourians deserve a proactive approach to this threat. The proposed criteria, blocked from proceeding further by the Clean Water Commission, would have provided a tool for monitoring and establishing health advisories in large, public recreational waters. They also would have provided clear guidance for those with private lakes concerned about the health impacts of cyanotoxins. MCE will continue to advocate for adoption of these criteria and urges the Clean Water Commission to reconsider their vote. 


Read the DNR Rulemaking Review for the proposed criteria

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