Portugal has a number of navigable estuaries, the most important being the Tagus, where the tide is felt 40km upstream of Lisbon. The only true inland waterway is the river Douro, canalised over a length of 211km to the Spanish border, with a series of five multi-purpose dams and locks. This development project was remarkable in featuring the highest shaft lock in the world at Carrapatelo (35m) when it was built in the 1970s. The entire length was opened to navigation in 1990. Although designed to carry iron ore down to Porto, the river has little commercial traffic, and is a spectacular waterway to cruise. At least one boat hire base has been established…