In 2016, water scientists from the Massachusetts Department of Conservation and Recreation (DCR) identified a fast spreading water plant in in Clamshell Pond as Brazilian Elodea (Egeria densa, also called Brazilian Waterweed). The plant was introduced to North America for use in tropical fish aquariums, but later spread to some natural water bodies. When it was identified in Clamshell Pond it was know to be present at a dozen or more sites in Massachusetts.
Brazilian Elodea in Clamshell Pond and Treatment in 2018
Brazilian Waterweed grows in dense mats that crowd out native plants and provide unsuitable habitat for native fish and wildlife. Because it can reproduce by fragmentation, it can spread easily by water fowl, boats, and fishing tackle, making it a threat to other water bodies. In the case of Clamshell Pond, it posed a particular threat to the Wachusett Reservoir, which lies less than a half mile away, as the duck flies. Recognizing the urgency of mitigating this risk, the Town of Clinton and Mass. DCR coordinated funding to destroy Elodia in Clamshell Pond.
Fortunately a low-dose herbicide was available that destroys Elodea without harming native water plants, fish, birds, or amphibians. The photos above show the state-licensed contractor deploying the approved herbicide in 2018. The effect was dramatic. Within weeks, the dense Elodia mats turned brown and decayed, while fish and wildlife remained abundant.
Since the initial treatment, state water scientist and Rauscher Farm volunteers routinely monitor the pond to ensure there is no significant re-growth.