Cyanobacteria (previously called blue-green algae) are ancient aquatic microorganisms that thrive in warm, calm, nutrient-rich surface waters. Certain cyanobacteria release toxins known as cyanotoxins. Exposure to these toxins through ingestion or direct contact with water has caused illness in animals and humans, including occasional dog deaths here on Cape Cod and elsewhere. Unfortunately, toxic algal blooms are becoming more common in Cape Cod’s freshwater ponds, and sufficient monitoring to protect public health is lacking.
Today, conditions that favor cyanobacteria growth and release of cyanotoxins are more common as water temperatures increase with the warming climate, and nutrients flow into ponds from overland runoff and underground septic systems. At the same time, growing scientific interest in cyanobacteria has yielded more knowledge about their dangers. The more we learn about cyanotoxins, the greater the concern about public health risks.
The Association to Preserve Cape Cod initiated a Pond Health Program in 2017 by testing an EPA-approved monitoring protocol for cyanobacteria. Our goal was to evaluate the protocol as a tool to forecast blooms and estimate toxicity. Working with partners from local pond organizations, municipalities, and scientists from the University of New Hampshire, our work resulted in identifying multiple toxic cyanobacteria blooms across the Cape so far this summer in prominent public recreational areas, including Brewster’s Mill Ponds, Barnstable’s Lake Wequaquet, Lovells, Bearses, and Shubaels Ponds; Mashpee’s Santuit Pond; Wellfleet’s Gull Pond; Chatham’s White and Stillwater Ponds; Harwich’s Hinckleys Pond; and Dennis’ Scargo Lake. There are undoubtedly many other undocumented blooms. The most common cyanobacteria we find here can produce hepatotoxins and neurotoxins that can cause damage to the liver and central nervous system. It is clear to us that the danger is more prevalent and potentially more harmful than we thought; monitoring the whole Cape is now urgent.
The issues of concern here are much like those we have seen in the marine environment: excess nutrients from septic systems and fertilizers. Solving the septic issue has proven to be a long and slow slog in the marine setting; the probability is this dynamic will be the same for the ponds. In the interim, homeowners anywhere, but especially those living close to ponds, would do well to eliminate fertilizers. Consider replacing (or minimizing) your lawn and shrubs with native species that not only provide habitat, but also don’t require the application of fertilizers and water. You can do your part on your property to protect water quality. And don’t forget to tell your Board of Selectmen that pond water quality needs to be a priority.