Great Bay National Estuarine Research Reserve, National estuarine research reserve in southeastern New Hampshire, United States.

Great Bay National Estuarine Research Reserve is a protected area along the southeastern coast of New Hampshire covering approximately 10,000 acres. It contains salt marshes, mudflats, tidal creeks, and eelgrass beds that form a diverse ecosystem supporting many species.

The reserve was established in 1989 as a research and protection area after plans emerged in the 1970s to build an oil refinery at the site. This conservation effort grew from increasing environmental awareness and the need to safeguard this important coastal zone.

The reserve grounds contain evidence of paleo-Indian settlements dating back 6,000 years and showcase the region's maritime development through colonial periods.

Visitors can use the Discovery Center with exhibits and educational programs, as well as explore the area on accessible trails. It helps to learn about the best seasons for birdwatching and tidal patterns, as these greatly affect what you can see.

The area monitors five major river systems that together form the largest estuarine network in the state. These river watersheds connect inland and coastal ecosystems in an uncommon way.