The Tijuana River National Estuarine Research Reserve is a state park and nature reserve in Imperial Beach, California. It features the Tijuana River Estuary, a small intertidal coastal estuary that is located between the borders of California and Mexico. It is also one of the few salt marshes that still exist in Southern California.

The Tijuana River National Estuarine Research Reserve is basically a shallow water habitat. Although it is an intermittent estuary, being left dry by droughts and overflowing after torrential rains, the reserve is still preserve to serve as a feeding, breeding, and nesting ground as well as key stopover point for 370 species of native and migratory birds.

Since it is off the beaten path, the Tijuana River National Estuarine Research Reserve is less known among other destinations in Imperial Beach. However, visitors can enjoy miles of walking trails here as well as some bird watching.