The Watertown Branch Railroad was a branch loop of the Fitchburg Railroad that was meant to serve the town of Watertown and the City of Waltham, Middlesex County, Massachusetts, as an independent short line railroad; it also serviced the Watertown Arsenal. The line has been formally abandoned and portions have been converted into a rail trail, the Watertown-Cambridge Greenway. A section from School Street to Arlington Street in Watertown was completed first. A small portion in Waltham has been converted into a park called Chemistry Station Park after the railroad station once located there. Construction of an extension to Fresh Pond Reservation in Cambridge began in the summer of 2018 and was completed in June 2022.^[1]

The railroad was chartered in 1846 and a second company, the Waltham and Watertown Railroad, was chartered to extend the line to the neighborhood just southeast of downtown Waltham, Massachusetts. In order to keep it out of the hands of its rivals, the Fitchburg took control of both companies before any track was laid and merged them into the Watertown Branch.

Construction began from West Cambridge^[2] in 1847. By 1849, the line ran to Watertown, with intermediate stops at Mount Auburn and Fresh Pond.^[3]: 154 In the Fresh Pond area it paralleled the existing Charlestown Branch Railroad which was used to haul ice.^[4] By 1851 it reached the Fitchburg's main line at the downtown Waltham station and the branch served as the main passenger line between Boston and Waltham. It was one of the few branch lines to be double tracked, as the line saw quite heavy traffic, especially in the 1880s and 1890s. The Boston and Maine Railroad took over the Fitchburg in 1900.

Competition from streetcars and automobiles cut heavily into inner-suburb passenger traffic. Minor stations were closed, including East Watertown in 1932.^[5] (The station was either later reopened, or never closed, as by 1938 it was the most-used station on the branch.)^[6] The B&M filed to abandon passenger service - by then a single early-morning round trip - in April 1938.^[6][7] Passenger service on the line ended on July 9, 1938, and the second track was removed by early 1940.^[8] The middle section of the line from the Waltham/Watertown line through Watertown Square to East Watertown was abandoned in 1960. This split the branch line in two, but traffic continued on both sides through the remainder of the 20th century. In 1991, about a half mile of track was abandoned on the west side of the line at Bemis, and the remainder of the line back to Waltham was abandoned in 2000.

On October 5, 2011, the Surface Transportation Board agreed to allow Pan Am Railways to abandon the final active 1.72 miles of the Watertown Branch from Newly Weds Foods in Watertown to the branch's junction with the Fitchburg Line between Sherman Street and Alewife in Cambridge. No freight had been carried for at least two years.^[9] As of May 2013, all but the approximately half-mile portion between Concord Avenue and the Fitchburg Line was in public hands.

State and local^[10][11] collaboration has been ongoing for transformation of the rail corridor into a rail trail,^[12] once known as the Charles River/Alewife Connector,^[13] now called the Watertown-Cambridge Greenway. The condition of the tracks at that time was deemed so poor that trains traveling at a mere 3 miles per hour (4.8 km/h) could derail.^[14]

In 1999, the Executive Office of Transportation purchased segments of the right-of-way from Guilford Transportation.^[15] This trail segment was later transferred administratively to the MDC, currently known as the Massachusetts Department of Conservation and Recreation (DCR).^[16]

On the east side of the branch, service was only to one customer, Newly Weds Foods, until service ended in 2007.^[17] The entire branch was then abandoned and out of service.^[16] Litter and downed trees were prevalent on the Fresh Pond–Watertown portion of the track before path construction began.

On May 22, 2013, the Massachusetts Department of Conservation and Recreation (DCR) and the City of Cambridge announced their acquisition of major portions of the remaining abandoned right-of-way from the railroad for $1.3 million plus an additional, unspecified amount from Cambridge, allowing completion of the Watertown-Cambridge Greenway. The DCR acquired the portion south of Huron Avenue, while the City of Cambridge now owns the right-of-way north to Concord Avenue.^[18]

In 2015, the DCR obtained $180,000 to fund design of the remaining greenway section, half from private donations. Public meetings were held on June 9 and November 30, the latter to present a 25% design for the greenway.^[19][20] A 75% design presentation was held on June 2, 2016.^[21] Funding of $3.6 million was approved by the Boston Region Metropolitan Planning Organization (MPO) in June 2017, with construction projected to start in Fall 2017 or Spring 2018.^[22]

The project was advertised for bids in September 2017 and bids were opened in March 2018. As of June, final design was complete. Construction started in late summer.^[1] The estimated cost is $3.182 million.^[23] As of mid-August 2018, the right-of-way had been cleared of most accumulated overgrowth and surveying work had begun. As of mid-October, track had been largely removed and several dozen trees with diameter greater than 6 inches were being removed due to poor health, safety concerns or construction conflicts. A formal Ground Breaking Event was held on December 5. As of June 2022, the full path is complete and open, with a formal ribbon cutting ceremony in planning.^[1]

• Concord Avenue - the rail line's non-gated and once busiest grade crossing
• At Fresh Pond's Kingsley Park (looking north), Feb. 2010
• Construction begins on Phase 1 of the Charles River to Alewife Connector multi-use path, July 2010
• Entrance to the Watertown Greenway, a bike trail along a portion of the Watertown Branch Railroad
• Entrance to Chemistry Station Park in Waltham, on the former site of Chemistry Station on the Watertown Branch in Waltham, MA.
• Excavator with rail removed from Watertown Branch for Phase II path construction, Sept. 2018
• Holworthy St ramp, the last entry point to be completed, open in May 2022

• Minuteman Bikeway
• Alewife Linear Park
• Charles River Bike Path