The Laguna Madre is a large shallow body of water separating Padre Island from the South Texas mainland. It is the largest of only six hypersaline coastal lagoons in the world. Hypersaline means that the water is saltier than seawater. This is beacuse the water evaporates faster than freshwater flows into it. This makes the Laguna Madre a negative estuary, one in which seawater flows in, rather than out.
The Laguna Madre covers 609 square miles and is fairly shallow with an average depth of about 2½ feet and is usually not deeper than 5 feet.
This unique environment has created one of the best recreational fishing areas in North America for redfish, black drum and speckled trout. The largest speckled trout caught in Texas waters are usually caught in the Laguna Madre and adjacent Baffin Bay.
Over many thousands of years, the drifting sand dunes in the center of Padre Island have almost closed the gap between the Island and the mainland. This mud and sand flat is known as the Saltillo Flats and has divided the Laguna Madre into what is now known as the Upper Laguna Madre and the Lower Laguna Madre. The channel that has been dug through this area for the intercoastal waterway is called the Land Cut
Almost 75% of its shoreline is protected by federal land (Padre Island National Seashore and the Laguna Atascosa National Wildlife Refuge) and private ranches (King Ranch and Kenedy Ranch).
This unique and beautiful ecosystem accommodates numerous protected (threatened and endangered) species, such as piping and snowy plovers, reddish egret, brown pelican, peregrine falcon, and white-tail hawk. It is also an important breeding ground for many aquatic birds, as well as an important wintering and stopover area for numerous species. It is home to approximately 80% of the North American wintering population of redhead ducks.
Some of the most extensive colonial water bird rookeries in Texas are located in the Laguna Madre and it accounts for almost 80 percent of all Texas seagrass beds.