Designated in 2000

Stretching along 15 km of the coastline of Santiago do Cacém and Sines municipalities, Lagoas de Santo André e da Sancha Nature Reserve is situated between the estuary of the river Sado and the cape at Sines, in Setúbal district. The Santo André and Sancha lagoons are separated from the sea by a narrow strip of dunes. The combination of marine, freshwater and land environments has led to a high degree of biological diversity and made this one of the main wetland areas in Portugal for migrating birds, particularly trans-Saharan passerines, herons and ducks.
Santo André is a coastal lagoon with brackish water and eutrophic characteristics, to control which it is artificially opened to the sea each year. It is home to a large breeding colony of coots Fulica atra and spoonbill Platalea leucorodia; squacco heron Ardeola ralloides and marsh harrier Circus aeroginosus are also regular visitors. It is also a nesting area and the main wintering site for the red-crested pochard Netta rufina. Sancha Lagoon is mainly fed by river water, and is populated by the common reed Phragmites australis and surrounded by typical dune vegetation, with low-growing scrub and stone pine Pinus pinea. Various bird species breed here, notably the purple heron Ardea purpurea. Among the various mammals that find these pools a suitable habitat is the otter Lutra lutra. Also worthy of note are certain plants endemic to Portugal, such as Linaria ficalhoana (a toadflax), Armeria rouyana (a thrift) and Ononis hackelli (a rest-harrow), and other species with high conservation priority such as violet cress Ionopsidium acaule and camphor thyme Thymus camphoratus.
Cultural and socioeconomic interest is limited, due to the decrease in the local resident population and to the kind of agriculture and forestry practised in the region. Nevertheless, there are some noteworthy cultural features, like the archaeological site at Cerradinha, a reminder of the human presence in the reserve in the Bronze Age, the traditional annual opening of the lagoon to the sea, and fishing, mainly for eels in Santo André lagoon.