What do cyanobacteria and their blooms look like?
The particular variety of cyanobacteria found at Spofford Lake exhibited on the shoreline as black or dark grey mats (not blue green algea) or as dispersed floating cells, most readily visible at beach areas, though they do exist naturally in open waters.
More commonly, cyanobacteria are known as blue-green algae and are photosynthetic bacteria. When growth conditions are optimal, high concentrations of cyanobacteria cells may form “blooms.” There is no official definition of a bloom in terms of cell density, but a key aspect is dominance of a single type of cyanobacteria.
Blooms sometimes appear as green or blue-green flecks scattered in the water, scums that float on the surface, or mats that rest on the bottom, but they can occur anywhere in the water column. Blooms that produce dangerous concentrations of cyanotoxins are known as harmful algae blooms (HABs), cyanoHABs, or harmful cyanobacteria blooms (HCBs) and can be dangerous to humans and their pets and wildlife.
If cyanobacteria are naturally present, what causes them to bloom and how long do they last? A number of factors create conditions for blooming and the creation of mats: 1) nutrient rich sediment, 2) elevated water temperature, 3) abundant sunlight, and 4) calm or stagnant water conditions. Once the blooms occur, wind and water movement carry the bloom to shore where they can accumulate. A bloom can last anywhere from a few days to a few months.
What adverse health effects might the cyanobacteria cause?
The most common effects are dermal itching and skin rashes. If ingested, by human or animals, vomiting and diarrhea may occur.
Should I take any precautions in cleaning my boats and other watercraft, and docks?
It is recommended that you clean your boat as you would for invasive species, like milfoil. Do so away from the lake so that any bacteria or other pests do not re-enter the lake.
If the bloom is on my beach, how should I dispose of it?
As contact with cyanobacteria may cause dermal irritation, wear protective clothing and bury it in a manner that dogs and small children will not come in contact with it.
Is cyanobacteria likely to impact wildlife, e.g, fish and birds?
The impact on fish and birds is unknown. Consumption of moderate amounts of lake fish filets (no organs or skin) by humans is not likely to be harmful. NH DES does not recommend eating lake snails.
Is the cyanobacteria likely to impact downstream areas, for example, properties on Partridge Brook?
While a definitive answer is not known, it seems likely that cyanobacteria entering the Brook would degrade in cooler months as it is doing at the lake.
How can the bloom be controlled or prevented in the future?
Algaecides are not permitted to kill the bloom so the best way to control or prevent the bloom over the long term is through continued and aggressive watershed management practices in the lake zone and the surrounding watershed. Reducing the amount of phosphate and other chemicals, including road salt, entering the lake is a key component to success.
At the urging of the SLA, The Town of Chesterfield and the NH DOT have reduced winter salting on most of the roads surrounding the Lake. Spofford Lake residents and homeowners in the watershed area can build on that success by using phosphorous-free fertilizers, e.g., Scott’s Turf Builder Winterguard 32-0-10 Lawn Food. (Look for a zero in the middle position).
Page updated May 10, 2021