The yellow lampmussel is an endangered species in Massachusetts, and is known to occur in only four rivers in New England; one of which is the Connecticut River. It is a medium to large sized oval-shaped mussel that it typically less than 5 ¼ inches in length and is characterized by a bright shiny yellow shell that is apparent in young, healthy mussels, but may darken with age. In its limited range in the Connecticut River, the yellow lampmussel has been found in areas ranging in depth from 3 – 30 feet, with low to moderate flows.
Working under its Threatened and Endangered Species Plan, and in consultation with various agencies and stakeholders, HG&E monitored yellow lampmussels within the area of the Holyoke Dam, starting 2003. Monitoring efforts included an annual survey of yellow lampmussels in the Holyoke Canal System as well a survey of the Holyoke impoundment and bypass reach occurring every three years. Note that the Holyoke impoundment includes the area of the Connecticut River bounded downstream by the Holyoke Dam and upstream by the Hatfield area, and the bypass reach is the area directly downstream of the Holyoke Dam.