The Beaver Brook Reservation is a state park and recreation area in Waltham, Massachusetts. It is noted for being the very first reservation that was created by the Metropolitan Parks Commission.

Established in 1893, the Beaver Brook Reservation goes way before a lot of other state parks in the country. It covers 59 acres of varying natural ecosystems like open fields, woodlands, and wetlands. It also contains fields, marshes, ponds, and even a cascading waterfall at its northern section. The southern portion of the park is more developed, outfitted with ball fields, tot lot, and a wading pool.

Due to its age, the Beaver Brook Reservation is also quite historic. It maintains the natural state of the area and takes visitors to the past with its restored 19th century fulling mill, the 1835 Robert Morris Copeland House, and a monument to the most famous trees of the 1890s, the Waverly Oaks.