One of the most notable features of the Nashua River is the Jackson Mills Dam, a hydroelectric project that was built in 1920 and provides fish passage for migratory species. The dam is located near Bridge Street, a busy road that crosses the river in Nashua. The river between the dam and the bridge offers scenic views of the city and its industrial heritage, as well as opportunities for recreation and wildlife observation.

A section of the Nashua River Walk is open from the Library past June Caron Park to the Temple Street Foot Bridge. The Jackson Mills Dam is on the river near the Library.

The Nashua River main stem forms the core of the Bolton Flats Wildlife Management Area and the Oxbow National Wildlife Refuge in Lancaster, Bolton, and Harvard where it winds north through marshy areas and former agricultural fields. Pepperell Dam in east Pepperell forms Pepperell Pond, an impoundment on the river popular for trophy large mouth bass and duck hunting. The river flows north through Hollis and Nashua, Hampshire where it joins the Merrimack River. The towns of Ayer and Pepperell have wastewater treatment plants discharging directly to the main stem Nashua River. The Devens Wastewater Treatment Plant has a sub surface wastewater discharge.

Nashua River Mainstem tributaries include Bowers Brook, Catacunemaug Brook, Flints Brook, James Brook, Mulpus Brook, Nonacoicus Brook, North Nashua River, South Nashua River, Still River, Unkety Brook, and Varnum Brook.