Tagus Estuary Natural Reserve is a natural reserve in Portugal. It is one of the 30 areas which are officially under protection in the country. The estuary of the Tagus River is the largest wetland in the country and one of the most important in Europe, a sanctuary for fish, molluscs, crustaceans, and especially to birds that stop-over on their migration between nort…Tagus Estuary Natural Reserve is a natural reserve in Portugal. It is one of the 30 areas which are officially under protection in the country. The estuary of the Tagus River is the largest wetland in the country and one of the most important in Europe, a sanctuary for fish, molluscs, crustaceans, and especially to birds that stop-over on their migration between northern Europe and Africa. It is the largest estuary in western Europe, with about 34,000 hectares, and regularly hosts 50,000 wintering waterfowl.