Imperial National Wildlife Refuge, Nature reserve along Colorado River, Arizona and California, US.

Imperial National Wildlife Refuge is a large nature reserve that stretches along the Colorado River between Arizona and California, protecting diverse habitats. The area includes wetlands, backwater lakes, and riparian forests that support numerous bird and fish species.

The refuge was founded in 1941 and covers 104 km² in La Paz and Yuma counties, Arizona, and Imperial County, California. It protects the last un-channeled 30-mile stretch of the lower Colorado River before Mexico. The 15,056-acre Imperial Refuge Wilderness is protected within it, and it surrounds Picacho State Recreation Area.

The Painted Desert Trail is a 1.3-mile self-guided National Recreation Trail, designated in 2005. It crosses terrain coloured by volcanic activity 30,000 years ago and gives a panoramic view of the Colorado River valley.

The visitor center provides information and is open on select days, while the natural areas are accessible during daylight hours. Visitors should bring plenty of water and prepare for extreme heat.

The refuge protects the last un-channeled stretch of the lower Colorado River before it enters Mexico, along with a federally designated wilderness of 15,056 acres that encloses Picacho State Recreation Area. Cottonwood and willow forests once lined these banks, sustained by natural floods; woodcutting in the steamboat era, clearing for agriculture, wildfire, salt cedar and flood-control dams have since reduced them, endangering the southwestern willow flycatcher.