In the NRPC region, both the Lower Merrimack River and the Souhegan River have been designated as protected rivers due to their outstanding natural and cultural resources. The Lower Merrimack River Local Advisory Committee formed in 1990 after the Lower Merrimack received designated status. Under RSA 483 Local River Management Advisory Committees are appointed for each designated river or segment. Activities of the Committees vary from reviewing wetland applications and site plans for development, to assisting with trail projects and commenting on conservation activities within the river corridor.
In 2008, NRPC and LMRLAC updated the Lower Merrimack River Watershed Management Plan
. Local involvement of the LMRLAC was crucial in order to develop a Management Plan that is consistent with the goals of each community in the Corridor and that provides a comprehensive action plan for the long-term management and protection of the Lower Merrimack River Watershed. An important part of the planning process involved a series of four river tours to identify areas of concern in each of the corridor communities.
In 2012, the NRPC conducted the Lower Merrimack River Continuity Assessment
to determine the level of aquatic habitat fragmentation resulting from bridges and culverts, to identify and prioritize the specific stream crossings that can be targeted for improvement, and to provide guidance on the long-term ability of the river's culverts to handle flow and sediment transport processes and their risk of failure.