The presence of the freshwater algae Didymosphenia geminata (a.k.a Didymo or “rock snot”) was recently observed by Dr. Caleb Slater, a fisheries biologist with the Division of Fisheries and Wildlife (DFW) during routine fisheries sampling on August 31, 2015 in the West Branch of the Westfield River in the town of Chester in Hampden County. DFW collected samples and made the preliminary identification which was confirmed by independent experts on September 2.

Didymo is a freshwater diatom that occurs in North America. The Division does not know how many streams in Massachusetts contain Didymo, as it is visually undetectable unless in bloom. Blooms may appear gray, brown, or white and has a texture of wet wool or cotton balls. Blooms, which happen only when certain conditions (including flow, nutrients, light intensity, and water chemistry) are present, can produce a dense covering on rocky substrate and eventually result in long stalks. Extensive Didymo blooms can temporarily cover river bottoms almost entirely. Didymo generally occurs in cold, clear, nutrient-poor waters with a neutral or slightly basic pH.

There is no known method for eliminating or controlling Didymo blooms. “Basically, the bloom has to run its course,” says Todd Richards, Assistant Director of Fisheries for the Division of Fisheries and Wildlife. “All recreational users should always thoroughly wash their equipment/clothing/waders/boats in hot, soapy water. Boats/equipment and other non-absorbent materials should be scrubbed. Soft, absorbent materials should soak in hot, soapy water for a minimum of 30 minutes. This is particularly important with felt-sole waders or other slow drying material such as sneakers, towels, and related items.”