Agua Hedionda Lagoon, Protected area in Carlsbad, California, United States.

Agua Hedionda Lagoon is a flat, blue-green body of water in Carlsbad, California, fed by Agua Hedionda Creek and separated from the Pacific by a long, low stone breakwater. A narrow sandy path bordered by low green and brown scrub runs along the near shore, and a dark rectangular floating dock rests near the right edge. Its Spanish name means "fetid water."

The lagoon was historically disconnected from the Pacific Ocean until dredging activities established a permanent connection around 1954, transforming its ecological characteristics.

The Agua Hedionda Lagoon Discovery Center hosts educational programs, bird hikes, and community events that foster environmental awareness among local families and school children.

Access is on foot via Bay Shore Drive, open to walkers from sunrise to sunset; vehicles may not drive through while it is closed to traffic. Alcohol is prohibited, and a vessel permit is needed to launch from the shoreline. Fishing is allowed from public shorelines, with a licence required from age 16.

Regular dredging operations remove approximately half a million cubic yards of sand every few years, benefiting both the lagoon's ecosystem and nearby beaches.