How to Restore Aquatic Habitat to Increase Fish Populations

Threatened species, such as the steelhead trout, have suffered a loss of habitat exacerbated by the drought.

Restoring California fish habitat is crucial to maintain native fish species as anadromous and other native fish populations decline in California rivers and streams. Drought conditions have exacerbated competition for dwindling water resources, increased aquatic habitat degradation, and contributed to invasions of non-native fish species.

Fish and other aquatic species require specific habitat for all life stages. Where the drought and other factors have wrought havoc, these aquatic habitats must be restored and enhanced to maintain/grow existing and historical aquatic communities. Additionally, restoring/enhancing river and stream habitats or native species will help them compete with non-native species, which exploit degraded habitat conditions and can quickly out-compete native populations

The approach to successful fish habitat restoration involves the following considerations.

What Drives Restoration Decisions?

Habitat improvement may take the form of creation or restoration. Creating new habitat where it did not previously exist is often required in association with project mitigation. Otherwise, where water exists, projects should focus on restoring/enhancing historical habitat functions including fish habitat.

Though numerous fish species are in decline (some more so than others), the native fish community that exists or was historically present in the project area will determine the specific enhancement activities needed to restore required habitat for all of a species’ life stages.

Five Steps to Successful Fish Habitat Restoration

Restoring fish habitat requires a robust and comprehensive approach. In addition to consulting with regulating agencies throughout the project lifecycle, following these five steps will help ensure project success.

  1. Determine project goals and objectives;
  2. Enlist experts to develop a constructible and sustainable design;
  3. Develop appropriate and tailored treatments for fish habitat, which may include:
    • Site re-contouring;
    • In-channel work, such as spawning gravels, riffles, runs, and pools;
    • In-stream woody materials and structures;
    • Biotechnical treatments; and
    • Native revegetation.
  4. Initiate physical construction, applying and adapting the design and treatments to the actual site conditions; and
  5. Conduct site establishment and long-term management that adapts for evolving site conditions.

HRS introduced woody debris, boulders, and other materials to a reach of the Truckee River to improve trout habitat and increase reproduction.

Successful Northern California Trout Restoration

Habitat Restoration Sciences (HRS), Dudek’s habitat construction subsidiary, recently completed work on flows within a reach of the Little Truckee River where trout habitat and population had significantly degraded. HRS’ extensive field experience informed the design, ensuring the project’s constructability and cost-effectiveness.

To improve trout habitat within the reach, HRS re-introduced large woody debris and boulders; excavated backwater pools for juvenile trout rearing; transplanted willows to provide shade and cover; and added spawning gravels to help wild trout reproduction.

Creating a restoration plan before beginning project work is critical. When contractors and project managers understand the project components and how they work together, and possess the tools to complete the job, there is a firm foundation from which to begin successful fish and aquatic habitat restoration.

John Zanzi is a landscape architect and construction manager with more than 30 years’ professional experience in design implementation for landscape projects, including ecosystem restoration, native plant revegetation, and wetland mitigation. For more information, contact him at or 916.438.5313.