NEGRO, Rio, a river of South America, forming the boundary between Patagonia and the Argentine Confederation, takes its rise in the Andes by two head-streams, one from the north and the other from the south, and flows eastward to the Atlantic, into which it falls in S. Lat. 41°, W. Long. 62° 50', after a course of from 500 to 600 miles.
It is full of small islands and sand-banks; and about the middle of its course it separates into two branches, which inclose an island of considerable size. The river is subject to two annual floods, one of which, in December and January, is occasioned by the melting of the snows of the Andes; and the other, in June and July, by the heavy rains in the interior. The river is about 2 miles broad at its mouth; but at the town of Carmen, about 16 miles from the sea, it does not exceed 300 yards in width. Near its entrance is a bar, over which there are several channels, some of which may be crossed by vessels drawing 11 feet of water. The climate of the district is healthy; and though very warm in summer, ice is frequently formed between the months of April and July. The winds are very variable, and frequently violent. The principal town on the river is Carmen, on the north bank, with a population exceeding 1000.