The archipelago of the Medes Islands is a group of islands that encompass a total area of 21.5 ha and is situated a mile off the Montgri Massif. It is an area of extraordinary importance, both biologically and ecologically due to the variety of species and environments it maintains.

There are a number of factors that make the Medes Islands such a rich and spectacular marine environment. The River Ter contributing organic matter along with the diverse composition of the marine substratum have a major effect. However, the influence of the northerly winds and currents that favour the entrance of deep water, rich in nutrients, also have a huge effect. All these influences produce an area of high biodiversity and productivity. The Medes Islands is home to some 1,345 species, both plant and animal.

Man has always exploited the abundance of the Medes Island. From the Romans through to modern times these rich fishing grounds were coveted. However, the 1950`s saw ecologists warning that the activities of both fishermen and coral hunters were becoming so intensive that many species should be considered endangered.

In 1983 the start of a protective regime was commenced by the Government of Catalonia. At that time the area became a closed season fishing area. Later, in 1990, the protection was increased. This protection covered the flora and fauna of the seabed. The passing of Law 19/1990 saw the creation of the largest Marine Natural Park in Catalonia and it is one of the most important in Europe.

All diving within the Medes Islands Marine Reserve is now strictly regulated and requires a specific licence.