Actually, it is practically impossible to tell the exact origins and development of this breed, since they only appear in a few historical documents even though they have been so common and so useful on the coasts of Portugal for centuries.

The first bibliographer to take up the study of the origins of Water Dogs was Dr. Manuel Fernandes Marques, a professor. He located the home of the Water Dogs in Mesopotamia, from which region the Phoenicians, a people who engaged in trade over a wide geographical area, spread them all over the world. The Phoenicians had already brought their dogs to the Iberian Peninsula, where they founded their trading posts, in 1250 B.C.

In 335 B.C., Alexander the Great conquered Asia Minor and Persia. In Persia, the sacred Zend-Avesta writings already made mention of the "canis turcus", or "great mongrel dog", as early as 600 B.C., the time of Zoroaster.

When the Romans occupied the Iberian Peninsula from 200 B.C. to 300 A.D., the ancient author Boethius made note of a "canis piscator", an ocean?fishing dog. At the same time, a dog clipped like a lion and called "canis leo" gained fame in Augustus Caesar's Rome. It is assumed that both of these dogs originated in Persia.

Around 300 to 500 A.D., the Visigoths under King Ataulf came from Russia to the Iberian Peninsula and mingled with the Romans. The Englishman James White (dates unknown) assumed that the dogs brought by the Visigoths came from Kirghizstan: In a valley cut off from the rest of the world, the Kirghiz had for thousands of years been using a dog morphologically identical to Water Dogs to herd their cattle. These dogs would then have developed into excellent workers due to the extreme temperatures and the demands of the herds. On the Iberian Peninsula the "canis leo" would then have cross-bred with the Kirghiz herd dogs.

From 700 to 1100 A.D. the Moors, an Arabian-Berber people, invaded the Iberian Peninsula from North Africa. Andalusia, today in southern Spain, and Algarve, now in southern Portugal, were conquered owing to the harbors the Romans had constructed, while what is today northern Portugal made room for the Swabians who had already settled there. The Moors brought the "Great Water Dog" from the steppes of Asia (southern Russia) and enabled it to spread throughout North Africa and the south of the Iberian Peninsula.