The Assabet River Rail Trail is a partially-completed multi-use rail trail running through the cities and towns of Marlborough, Hudson, Stow, Maynard, and Acton, Massachusetts, United States. It is a conversion of the abandoned Marlborough Branch of the Fitchburg Railroad that’s right-of-way parallels the Assabet River in the trail’s midsection. When fully completed, the end-to-end length will be 12.5 miles. Efforts to develop the trail are spearheaded by the all-volunteer, non-profit organization Assabet River Rail Trail, Inc.

In 1851 Henry David Thoreau wrote in his famous journal about a trek to Boon’s Pond—today known as Lake Boon located in the towns of Stow and Hudson—which on the return included a walk along the railroad tracks now replaced by the trail.

There are four boat launches providing canoe and kayak access to the Assabet River along the trail: one in Hudson at Main Street Landing; one in Stow at Magazu Landing; and two in Maynard, at White Pond Road and Ice House Landing.