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Instream Flow

Ensuring that New Hampshire’s 19 designated rivers have enough water for both people and aquatic life.

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Click on the image to view the program video.

The Instream Flow Program ensures that rivers continue to flow in spite of the uses and stresses that people put on them. Under natural conditions, rivers flow freely with source waters coming from precipitation via lakes, ponds, wetlands, small streams and groundwater. Under human influences, however, river dynamics can change drastically. People frequently withdraw large amounts of water for drinking and irrigation directly from rivers, as well as from the sources that supply the rivers, particularly lakes and groundwater. Land use changes can result in faster runoff and changes to the stream structure. Many rivers have dams that restrict the amount and timing of water flowing downstream. In addition, the loss of wetlands to land development reduces the amount of water that would normally augment rivers during dry periods. These changes in stream flow can impair river habitat. The Instream Flow Program operates within the New Hampshire Rivers Management and Protection Program statute, Section 9-c (RSA 483:9-c) and in accordance with Administrative Rule Env-Wq 1900.

The program determines the seasonal flows necessary to support both natural aquatic habitats and human uses and then works with water users and dam owners to ensure that their water needs are met while maintaining the protected flows during periods of unusually low flow, even during droughts. The program annually performs a wide range of field activities to collect the environmental data necessary to develop protected instream flow values and evaluate the success of instream flow management; the program’s 2021 Work Plan summarizes those field activities.

Currently, two rivers, the Lamprey and Souhegan Rivers, are actively managed under the Instream Flow Program. In addition, protected instream flows are being developed for the Cold and Warner Rivers, and will soon be under way for the Ashuelot River.

Protected Instream Flow Studies In Progress

The protected instream flow studies of the Cold and Warner Rivers are under way. Protected instream flows are criteria that define a stream flow pattern and maintain water for instream public uses and aquatic wildlife, and meet water quality standards. A public hearing on the draft protected instream flows for each river will be scheduled when its draft Protected Instream Flow Study Report is published. NHDES is also working with water users and dam owners along these rivers to determine water use needs and current practices to develop Water Management Plans that balance human needs with the needs of aquatic life identified by each protected instream flow study. A public hearing on each draft Water Management Plan will be scheduled when they are completed.

    a map of the protected area around the ashuelot riverAshuelot River Study

    The protected instream flow study of the Ashuelot River began in 2021. The draft protected instream flows and the draft Water Management Plan for the Ashuelot River are estimated to be complete in 2024.

    Real Time Water Data


    a map of the cold river watershedCold River Study

    The protected instream flow study of the Cold River began in 2019. A draft Protected Instream Flow Study Report – Cold River is now available for public review. NHDES’ consultant, Gomez & Sullivan Engineers Inc., completed the protected instream flow study of the Cold River and summarized the results in the draft report. The public is invited to review and comment on the report. NHDES will hold an Informational Meeting describing the report on Monday, September 27, and a Public Hearing on the draft protected instream flows is scheduled for Monday, October 18. Both meetings will begin at 7 PM at the Alstead Town Hall, 9 Main Street, Alstead, NH. A comment period will remain open until November 17, 2021, at 4 PM. The draft Water Management Plan for the Cold River is being prepared, with public review and release planned for later in 2021. Comments may be submitted to Wayne Ives, Instream Flow Program Coordinator, PO Box 95, Concord, NH 03302-0095, or to

    Real Time Water Data

    Learn more about the Cold River  

    a map of the Warner River watershedWarner River Study

    The protected instream flow study of the Warner River began in 2020. Public hearings on the draft protected instream flows and the draft Water Management Plan for the Cold River are planned for 2022.

    Real Time Water Data

    Learn more about the Warner River  

    Protected Instream Flow Values Established – Flow Management Under way

    The instream flow pilot study was completed in 2015 on the Lamprey and Souhegan rivers. The Report of the Instream Flow Pilot Program summarizes how the protected instream flows and water management plans were developed for each river, and makes recommendations for applying instream flow management on other New Hampshire rivers designated under the Rivers Management and Protection Program.

    Future River Studies

    The Ashuelot, Cold and Warner Rivers were identified on the 2018 Priority List for future protected instream flow studies. With studies under way for the Cold and Warner Rivers, the Ashuelot River is the next target for implementation of the Instream Flow Program. The protected instream flow study of the Ashuelot River will commence in 2021. Beginning in Winter 2020, NHDES has been working with stakeholders to identify the next rivers as priorities for protected instream flow studies. Please contact us if you have thoughts regarding priority rivers for instream flow protection.


    Target Fish Communities

    A goal of the Instream Flow Program is to ensure that flows in each river are suitable for the fish that should live in that river. Therefore, there is a target fish community report for each river. The target fish community reports include the fish species population distributions that should be found in each designated river.

    Estimating Historical Stream Flows

    The Instream Flow Program requires at least 30 years of historical stream flow data, but this is not available for every river. Flows can be estimated by comparing nearby gaged rivers and adjusting for watershed area and geography.

    Inforation Icon

     Need more information? 

     Need more information? 

    All of the New Hampshire Instream Flow Program documents available online can be found here. If you still do not see what you are searching for, contact us for more information.

    Instream Flow Program Coordinator
    Instream Flow Environmentalist