California Department of Fish and Wildlife

Instream Flow

What is Instream Flow?

Big Sur River

The term "instream flow" is used to designate a specific stream flow, measured in cubic feet per second (cfs), at a particular location for a defined time, and typically follows seasonal variations. Instream flows are needed to protect and preserve resources, such as fish, wildlife and recreation, in a waterway. Instream flow recommendations, based on scientifically defensible assessments, are developed to inform the state regulatory process with respect to water resources. Five riverine components (biology, hydrology, geomorphology, water quality and connectivity) are used to prescribe instream flow through the Instream Flow Incremental Methodology (IFIM) process.

Role of the Instream Flow Program at CDFW

As trustee for California’s fish and wildlife resources, CDFW has jurisdiction over the conservation, protection, and management of fish, wildlife, native plants, and habitat necessary for biologically sustainable populations of those species. Certain fish and wildlife rely upon stream-related ecosystems, which in turn are reliant on adequate instream flows. CDFW is mandated to develop flow criteria for rivers and streams throughout the state. Minimum flow levels are established to assure that stream flows are maintained at levels which are adequate for long-term protection, maintenance and proper stewardship of fish and wildlife resources. The CDFW Instream Flow Program (IFP) was developed to determine what instream flows are needed to maintain healthy conditions for fish and wildlife. The IFP develops information on the relationships between instream flow and available stream habitat. With this information the IFP determines if instream flows are adequate, and prescribes appropriate instream flows for a waterway if they are not. These flow recommendations are transmitted to the State Water Resources Control Board (State Water Board) for their consideration in water allocation and appropriation actions, used in other regulatory, legal or collaborative proceedings related to appropriation of water or other water planning activities.

Program Structure & Key Activities

As part of the Water Branch’s Statewide Water Planning Unit, the IFP provides scientifically defensible and comparable instream flow recommendations for water acquisition, water rights, and statewide water planning processes. CDFW’s stream flow assessment activities encompass a multi-disciplinary team with headquarter and regional components, including a professional staff of biologists and hydraulic engineers throughout the state. The IFP headquarters staff oversees study design and implementation, collects field data, and coordinates program implementation with CDFW’s Regions, State Water Resources Control Board, U.S. Fish and Wildlife Service, and non-governmental organizations. CDFW Regional staff identifies stream study priorities, oversees study implementation, and conducts field data collection.

Anticipated projects will inform: relationships of flow to aquatic habitat, aquatic habitat suitability, stream temperature, channel geomorphology, riparian habitat and restoration activities; the temporal and spatial hydrologic characteristics of flow regimes; fish population abundance, distribution and dynamics; and aquatic invertebrate production.

Key activities include:

  • Conducting instream flow studies ranging from site specific hydraulic analyses and habitat suitability investigations to flow studies using IFIM.
  • Preparing Requests for Proposals for specific instream flow investigations.
  • Preparing defensible flow recommendations, including addressing important life history information needs for spawning, rearing and migration of threatened and endangered anadromous fishes.
  • Managing projects to collect, obtain, analyze, and provide credible scientific information which can be applied in water planning and regulatory arenas.
  • Developing Quality Assurance and Quality Control (QA/QC) guidelines, including Standard Operating Procedure documents.

Instream Flow Links

Instream Flow Council

CDFW Instream Flow Recommendations

State Water Resources Control Board Instream Flow Recommendations


Instream Flow Documents

Instream Flow Program FAQ Sheet - Fall 2013 Update (PDF)

Instream Flow Standard Operating Procedures

Instream Flow Program Annual Reports

Priority Streams List, 2008 (PDF)


Study Plans

Flow Recommendations

Historical Flow Studies

For more information, contact Diane Haas at Diane.Haas@wildlife.ca.gov or (916) 445-8575.