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Strange Cyanobacterial Blooms

Date: November 01, 2020

This year has been unusual to say the least. It seems that what people needed the most was a good getaway to relax, and enjoy the nature and beauty of New Hampshire. As a result, the lakes of New Hampshire were heavily recreated during the summer of 2020. With more eyes on the water, however, NHDES received many reports this year of strange sightings in our lakes. Among the anomalies reported were cyanobacteria blooms (formerly called blue-green algae) in a variety of unusual colors and shapes. The newly established NHDES Harmful Algal (Cyanobacterial) Bloom Program was officially started in 2020 to help respond to public concerns about the increasing prevalence of cyanobacteria.

Cyanobacteria blooms are a common occurrence worldwide and occur when cyanobacteria undergo rapid growth. Eventually the cells rise in the water column toward the surface. The surface scums can typically appear green or blue-green, but can also display a wide range of colors depending on the type of bloom. The build-up of cells presents a threat to public health, as increases in potentially toxic cyanobacteria concentrations often contain higher levels of toxins known as cyanotoxins.

While we usually associate blooms with increased nutrients and temperatures, there are several factors that contribute to a bloom. It can be difficult to diagnose, as each lake is so unique and there is a delicate balance of biotic and abiotic conditions that can support cyanobacterial growth. Some blooms may be triggered by rain events, followed by hot sunny days. Other lakes may bloom under hot, stagnant conditions. Some lakes have blooms for a few years and then sometimes the blooms seem to be gone for several years. It can be difficult to predict. There are thousands of different cyanobacteria taxa and they each have their own growth requirements, habitats, niches, toxicity and colors.

A recent cyanobacterial-scum oddity had us wondering. A black mat of cyanobacteria was found washing along the shores of Spofford Lake. While we first speculated that it was an accumulation of debris and muck, samples of the black sludge revealed cyanobacteria mats. Our next hypothesis was that we were seeing Lyngbya wollei, a tropical-subtropical taxon well known for its growth of toxic, black mats. The Spofford Lake Association had samples sent to Green Water Laboratories in Florida for further analyses. The identification was a mix of Stigonema, Scytonema and Tolypothrix; a variety of cyanobacteria taxa that form benthic mats and appear black. The genetic (DNA) analyses of these mats will also be determined by a research group/course with Keene State under Dr. Loren Launen. As we continue to learn more about this black mat, NHDES remains cautious and advises that people leave this material alone and allow it to naturally degrade.

Another remarkable cyanobacterial bloom occurred on Tucker Pond. Woronichinia had bloomed much of the summer, displaying an array of cloudy, tan and orange-ish streaks across the lake. We were mystified, however, when a photo of an orange blob was shared with us. Upon sampling, the blob (which appeared structural) dissipated into a cloud. The sample showed us that a combination of the Woronichinia (cyanobacteria) and Botryococcus (green-algae) had formed an amorphous orange surface blob. Aside from that strange finding, the duration of the Woronichinia bloom surprised us as we continued to observe the odd-colored bloom as late as October.

The NHDES Harmful Algal (Cyanobacterial) Bloom Program would like to remind the public that blooms can often surface well into the late fall, with records of some lasting until ice cover. While the swim season is over, visiting the shorelines where blooms accumulate can also be harmful to those who make contact with potentially toxic cyanobacteria. Always look before allowing your children or pets in the water. Not all cyanobacteria are toxic, but many of them are and can produce toxins under unpredictable conditions. With the large range of cyanobacteria and cyanotoxins that exist, NHDES advises lake-goers to avoid contact with anything suspicious, colorful, scummy, or turbid in the water. Advisories are a reminder to remain cautious around these blooms. Please take photos if you think you see a bloom or have questions about something unusual in the water. Report your findings to, or contact us at (603) 848-8094.