The third expedition by Columbus in 1498 was the beginning of the first successful Castilian (Spanish) colonization in the West Indies, on the island of Hispaniola. Despite growing doubts, Columbus refused to accept that he had not reached the Indies. During the voyage he discovered the mouth of the Orinoco River on the north coast of South America (now Venezuela) and thought that the huge quantity of fresh water coming from it could only be from a continental land mass, which he was certain was the Asian mainland.