In 2018, the Department of Conservation and Recreation (DCR) opened a new $1.5 million footbridge over the Charles River, just upstream from Watertown Dam. The bridge connects the north and south branches of the Blue Heron Trail between Galen Street and Bridge Street. This Watertown Tab article discusses the construction of the bridge.
The Joseph Thompson Footbridge replaced an older bridge by the same name, which honored a soldier who died during World War I.
The old bridge had such a steep slope that it was dangerous for people using wheelchairs or pushing strollers.
The footbridge is included in the Wikipedia list of Charles River crossings.