The Environmental Protection Agency (EPA) has clarified its Clean Water Act (CWA) guidance for waters impaired by hydrologic alteration (HA). This is a positive step forward that can lead to flow restoration or avoiding new flow alteration impacts such as dewatering of streams and habitat destruction.

The Basics The CWA serves to protect the chemical, biological and physical quality of a waterbody. HA directly affects the physical quality of streams, wetlands, and other waterbodies. Historically, rivers that have been impaired due to hydrologic alteration were not recognized as such by water quality agencies. In order to fully address and implement effective restoration and conservation efforts of these waterbodies, it is essential to identify rivers and streams impaired by HA. In addition, HA can affect the chemical and biological quality of the waterbody and prevent waters from meeting water quality standards. HA can also impair the Designated Uses, another cornerstone of the CWA, including aquatic life, recreation, drinking water and cultural uses.

Common Causes of Hydrologic Alteration

 Low head dams

 Surface and ground water withdrawals

 Hydropower dams and operations

 Diversions

 Water storage reservoirs

 Impervious surfaces and stormwater

 Channelization

 Interbasin transfers

Take Action!

Anyone can submit documentation of waters impaired by HA to state and tribal agencies for their 2018 biennial reports. Important information to include in submittals is evidence of HA through USGS gage or other flow records, photographs, personal testimony and demonstration of impaired designated uses. Documentation for listing HA waters should be submitted to state or tribal water quality agencies, and EPA regional offices.

Contact information and submission deadlines can be found at

A template for submitting HA documentation is found at