Prevention and Restoration of Hydrologically Altered Waters

Working across all CWA programmatic lines to identify and restore hydrologically altered waters, as well as preventing future alterations.

On this page:

• About the Program
• Types of Assistance
• How This Program Helps Build Resilience
• Connections to Other EPA, Federal, or Non-Governmental Efforts

About the Program

According to U.S. Geological Survey (USGS), the majority of the nation’s water bodies have human-made alterations including dams, diversions, stream crossings/culverts, canals, surface water and groundwater withdrawals, and impervious cover. These alterations can cause changes to salinity, temperature, dissolved oxygen, nutrients and sediment transport, and natural flow regimes (including extreme low and high flows) and create barriers to fish and aquatic life passage. USGS states that this type of pollution may likely be the primary cause of ecological impairment in river and stream ecosystems in the United States. Scientific studies conclude that climate change will exacerbate those effects.

Understanding and identifying impairments due to this type of pollution can provide opportunities to restore these waters and provide increased resilience to a changing climate. Restoration through dam removal, dam re-operation, green infrastructure, and properly designed stream crossings improves water quality and natural hydrology; reestablishes natural temperature, salinity, and sediment transport regimes; removes barriers to fish passage; and in some instances increases land building in coastal zones. Multiple CWA programs address restoration and prevention of further degradation.

Types of Assistance

The EPA has clarified how CWA programs can address water quality impacts related to hydrologic alteration. These updates provide an overview of the latest scientific information on the impacts of this pollution on aquatic life, created tools to prevent future alteration while meeting societal water needs, and developed guidance and information on how to restore hydrologically altered waters, including providing potential funding sources for such restorations.

Technical Assistance

The EPA’s updated scientific information and technical tools include the following:

• The Final EPA-USGS Technical Report: Protecting Aquatic Life from Effects of Hydrologic Alteration (pdf) is the result of the EPA partnering with USGS on a comprehensive overview of the state of the science on the impacts of hydrologic alteration on aquatic life, including how restoration of these waters provides resilience in a changing climate. The document includes an appendix for states and tribes titled “Climate-Change Vulnerability and the Flow Regime.”
• The EPA published Best Practices to Consider When Evaluating Water Conservation and Efficiency as an Alternative for Water Supply Expansion (pdf) to assist local governments and utilities in understanding best practices as alternatives to meeting water demand by building new reservoirs that can alter stream temperature, flow, and dissolved oxygen; increase nutrients; disrupt sediment transport; and impair aquatic life passage.
• In the 2016 Integrated Reporting Guidance (pdf) (pp. 13–16), the EPA clarified how to identify waters impaired due to hydrologic alteration. EPA noted that pollution, such as hydrologic alteration, was a significant issue and one that would be exacerbated by climate change. Many states are using that guidance to update their assessment and listing methodology to ensure that they address impairments due to pollution and look for opportunities to restore waters through dam removal, dam re-operation, and green infrastructure as an alternative to total maximum daily loads (TMDLs).
• The EPA published the Frequently Asked Questions on Removal of Obsolete Dams (pdf). Removing obsolete dams restores connectivity; naturalizes flow, temperature, and sediment regimes; reduces eutrophication; improves water quality; and may reduce the methane emissions of impounded waters. This FAQ discusses the water quality, public safety, and ecological benefits of dam removal, as well as potential funding sources.
• EPA Region 4 partnered with federal agencies (including U.S. Army Corps of Engineers [USACE], U.S. Fish and Wildlife Service, and Natural Resources Conservation Service), state agencies, non-governmental organizations (NGOs), universities, and citizens to develop state-specific information on dam removal, available online as the Georgia Dam Removal Handbook, to clarify the permitting process for dam owners and project managers.

Convening Assistance

• Information on effects of hydrologic alteration and opportunities to restore hydrologically altered waters are provided to states, tribes, and territories through regular communication and annual workshops across all programmatic lines, including Water Quality Standards, Wetlands Program (Clean Water Act Section 404), and the Restoration and Watershed Planning Program (Clean Water Act Section 303(d)/305(b) for TMDLs and Listing, respectively), as well as at national or regional meetings of professional groups and organizations.
• EPA Regional Offices partner with other federal and state agencies, as well as universities and NGOs, through state-based Aquatic Connectivity Teams in Georgia, South Carolina, North Carolina, and Florida to address impacts of hydrologic barriers, including dams and improperly constructed stream crossings.

Outreach and Education Assistance

• The EPA provides resources to help states, tribes, NGOs, and citizens access information on the water quality impacts of hydrologic alteration and learn how restoration and prevention provide resilience to climate change.

Financial Assistance

• The program has developed documents to provide information on EPA grants support specific types of restoration. For instance, the FAQ on Removal of Obsolete Dams describes where CWA Section 319 grants have been used for dam removal to improve water quality; the requirements to be eligible to use Five Star and Urban Water Grants for removal; and example cases in which states have used Wetlands Program Development Grants to study the impacts of low-head dams to develop their in-house technical expertise or conduct scientific studies on the impacts of dam removal.

How This Program Helps Build Resilience

Preventing hydrologic alteration or restoring hydrologically altered waters can provide resilience in numerous ways, as well as offer many societal co-benefits.

• Removing dams restores the natural flow, sediment, and temperature regime; improves water quality; may reduce methane; and may increase land building in coastal zones.
• Requiring more naturalized stream crossings, such as properly sized, open-bottomed crossings that act as part of the stream or river, allows flood flows and debris to pass in storms. Restoring poorly designed culverts and properly sizing and designing new culverts provides resilience and protects public safety during extreme weather events, saving costs for communities over the long term.
• Restoring naturalized flows through green infrastructure, dam removal, or dam re-operation support the freshwater flows that are critical to the ecological function of estuaries.

Connections to Other EPA, Federal, or Non-Governmental Efforts

• USACE developed a nationwide permit specifically for removal of low-head dams prompted by strong support and increased interest in restoration of rivers and streams through obsolete dam removal.
• America’s Water Infrastructure Act of 2018 included the reevaluation of the need for certain dams and urged the inclusion of “Alternative Measures for Aquatic Ecosystem Restoration,” such as natural and nature-based features to carry out a project to restore and protect aquatic ecosystem or estuaries, and the use of natural infrastructure for flood risk management or hurricane and storm damage risk reduction.
• NGOs have prioritized restoration of hydrologically altered waters through efforts such as dam removal, retrofitting undersized stream crossings, and the re-operation of dams, successfully seeking out partnerships with state and local governments to complete those restorations. This approach is also supported by communities that have identified restoration of hydrologically altered waters as a high priority for becoming “river-smart,” preparing for extreme weather, and protecting public safety.