“Rock Snot” Found in Westfield River, MA



The presence of the freshwater algae Didymosphenia geminata (a.k.a Didymo or “rock snot”) was recently observed by a fisheries biologist with the MA Division of Fisheries & Wildlife (DFW) 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.

This is the second occurrence of Didymo in the state documented by the Division. The first occurrence was in 2013 in the Green River in Alford and Egremont. The Green River algae bloom began in May of 2013, lasted only a short time and had no detectable impact on the resource. Didymo was virtually undetectable in samples collected later in the summer of 2013, and no visible blooms have been found in the Green River by the Division since that time.

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. Conditions typical of the Upper Westfield River drainages should greatly limit the occurrence of Didymo blooms.

The frequency and intensity of Didymo blooms vary widely between watersheds because of differing environmental conditions. In the Northeast, Didymo blooms have been observed in NH, VT, CT, NY, PA, VA, MD and WV. In Massachusetts, there have been no reported changes to fisheries resulting from the few Didymo blooms. Whether Didymo was always present in the waters where blooms have occurred or is a recent introduction is unknown. 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.”