Wetlands Mitigation

Protecting, enhancing and restoring wetlands and streams to compensate for impacts to aquatic resources.

The sky is reflected in water surrounded by plants and trees.When aquatic resources are removed from the landscape the important functions they perform are also lost. Even after avoiding and minimizing impacts, there are some projects that result in a loss or degradation of wetlands and streams. The goal of compensatory mitigation is to sustain these functions at the watershed scale for the long-term. Mitigation projects are selected and designed to offset these losses by means of land protection, restoration, and enhancement to wetlands and streams.

When mitigation is required

After avoidance and minimization to aquatic resources has been achieved through project location and design, mitigation is required for:

  • Permanent impacts to freshwater wetlands of 10,000 square feet or more.
  • Any permanent impacts to tidal surface waters, tidal wetlands, the tidal buffer zone, or sand dunes, excluding several project-specific exemptions.
  • Projects classified as major impacts to intermittent and perennial streams, including new channel and bank impacts over 200 linear feet and Tier-specific stream crossings.
  • Pond construction with over 20,000 square feet of impact in a wetland or surface water.
  • Docks and new shoreline structures that have 2,000 square feet or more total frontage on the waterbody.
  • Any permanent impact to a Priority Resource Area, regardless of the size, that remains after additional avoidance and minimization measures have been taken.

Once it is determined that mitigation is needed to offset unavoidable impacts, there are two options available to permit applicants:

Permittee-Responsible Mitigation: The permitee will provide a restoration, enhancement, or land preservation project to compensate for the impacts from a specific project. The permittee is responsible for the design, implementation, monitoring, and continued success of the mitigation site. This type of mitigation may occur at the same location as the impacts or off-site within the same watershed. The applicant should consider priorities identified by the town’s conservation commission as an option.

In-Lieu Fee Payment to the Aquatic Resource Mitigation (ARM) Fund: If there are no suitable, local projects that can be found to offset losses to aquatic resources, then the permittee can make an In-Lieu Fee (ILF) payment into the ARM Fund. NHDES will determine payment amount using the ARM calculator that is published annually. Fees collected by the ARM Fund are made available as grants to support projects that will offset the functions and values lost in the watershed. 

Mitigation Steps

Pond surrounded by treesImpacts to wetlands and streams need to be avoided and minimized

Because wetlands and streams provide important functions to wildlife, humans, and the overall environment, impacts to these resources need to be avoided and minimized to the greatest extent practicable.

Avoidance and Minimization Best Management Practices   

A stream flows over rocksExplore Local Mitigation Opportunities

A permit applicant should consider local conservation projects prioritized by the town that may be used as permittee-responsible mitigation. The town Conservation Commission is responsible for creating a “Mitigation Priority List.”

What makes a good mitigation project  

Rocky shore of a lakeMake an In-Lieu Fee Payment

If there are no suitable, local mitigation projects, then the applicant can make a payment into the Aquatic Resource Mitigation Fund. NHDES will determine the amount of the payment required to compensate for wetland and stream impacts using the ARM calculator.

View the ARM ILF Calculator  

Types of Mitigation Projects

There are different approaches that can be used to compensate for lost functions from wetland and stream impacts, and they may be used singly or in combination.

Upland Buffer Preservation

This is the permanent legal protection of a valuable wetland or stream and its upland buffer. The protection will ensure that the waterbody and its surrounding upland area, will remain in a natural and undeveloped condition in perpetuity. Protection is accomplished by placing the land under a conservation easement, which is held by a conservation organization, town, or state agency. Land preservation does not make up for lost wetland functions and values, but removes the threat of future loss and degradation.


These are activities that will return a degraded wetland or stream back to its natural condition.

  • Examples of wetland restoration are removing fill and replanting hydric plants, restoring the natural hydrology of a wetland by removing ditches and drains, and creating living shorelines in tidal areas where erosion and armoring have impacted the marsh migration and tidal flushing.
  • Examples of stream restoration include removing aquatic barriers such as dams and culvert to bring back the river environment, daylighting buried streams, removing hard armoring and using bioengineering to stabilize banks, improvements for fish and wildlife habitat, and reconnecting the floodplain.


This is when certain aspects of the physical, chemical, or biological characteristics of an aquatic resource are modified to increase its functions. Enhancement is usually designed to target a specific improvement.

  • For example, a perched culvert may be upgraded to an open-bottom arch to enhance fish passage and hydrology at a site.
  • Riparian plantings in the buffer to improve water quality and wildlife habitat functions.  

Establishment (Creation)

This is a man-made wetland that involves excavating an upland area to achieve adequate hydrology to support hydric soils and vegetation. Wetland creation is not a preferred method of mitigation to be used in New Hampshire based upon previous failures of wetland creation, the high costs for these projects, and significant engineering efforts needed to succeed.

Aquatic Restoration Mapper

Use this interactive mapping tool to target potential mitigation projects to improve stream connectivity, restore important fish habitat and increase flood resiliency.

Program Specialist
Wetland Mitigation Coordinator