The Laguna Madre is a long, shallow, hypersaline lagoon along the western coast of the Gulf of Mexico in Nueces, Kenedy, Kleberg, Willacy and Cameron Counties in Texas, United States.

As a natural ecological unit, the Laguna Madre of the United States is the northern half of the ecosystem as a whole, which extends into Tamaulipas, Mexico approximately 144 miles (232 km) south of the US border, to the vicinity of the Rio Soto La Marina and the town of La Pesca, extending approximately 275 miles (443 km) through USA and Mexico in total.

Laguna Madre was formed about 3,000 years ago, after the stabilization of the sea level on the Texas Coast, culminating in the rise of Padre Island.

The Baffin Bay extension is considerably older than Laguna Madre, and formed as a river valley during the Pleistocene epoch, over 12,000 years ago.

The city was named Port Isabel in 1928, and in 1954, the Queen Isabella Causeway, the longest bridge in Texas, was constructed across Laguna Madre to South Padre Island.

A newer bridge was built in 1974,[6] but part of it collapsed on September 15, 2001, after being hit by a barge, causing eight people to plunge to their deaths and significantly hindering the economy of South Texas.

It was named after United States Congressman Joseph J. Mansfield (D-TX), who introduced the bill that extended the Intracoastal Waterway from Corpus Christi to Brownsville in the 1940s.

The western shore, a large part of which is included in the King Ranch, is usually marked by sand dunes, yucca, prickly pear, century plants and an occasional oak tree bent by the wind.

[6] Included in the Lower Laguna Madre is Red Fish Bay, which is found along the shoreline of the King Ranch, south to Port Mansfield.

[14] The reasons for the lagoon's hypersalinity include its isolation from other bodies of water, the lack of a significant river source, and a high rate of evaporation caused by its shallowness and dry climate.

Its salinity was even greater before the Port Mansfield Gulf Channel was dredged on Padre Island, which allowed a larger amount of seawater exchange.

Other birds in the area include the peregrine falcon, piping plover, roseate spoonbill, long-billed curlew, crane, egret and the brown pelican.

Activists have likewise railed against a proposed wind turbine farm off Baffin Bay, due to the potential harm to the scenic shores and the bird populations.