The Carmel River Lagoon, located at the mouth of the Carmel River in Monterey County, is a small but ecologically important bar-built estuary. Separated from the Pacific Ocean by a dynamic sandbar, the lagoon experiences seasonal changes in water levels, salinity, and habitat conditions. During the rainy season, increased river flow can breach the sandbar, allowing tidal exchange, while in drier months the lagoon often becomes isolated from the ocean, leading to freshwater buildup and fluctuating water quality.

This estuarine system supports a variety of habitats, including open water, riparian vegetation, and marshlands that provide critical feeding and nursery grounds for fish, waterfowl, and amphibians. Species like steelhead trout rely on the lagoon as a transitional habitat between freshwater and the ocean.

Water level monitoring at the Carmel River Lagoon helps track the timing and impacts of sandbar breaching, informs flood risk management, and supports ongoing restoration efforts aimed at balancing ecological health with public safety in this sensitive coastal system.