I. The principal river of British Guiana, rises in the Acaray mountains near the S. limit of the country, lat. 1° 30' N., Ion. 57° 11' W., traverses it in an almost northerly direction, and falls into the Atlantic by an estuary 30 m. wide at its mouth, about lat. 7° N., Ion. 58° 30' W. Its course is interrupted by numerous cataracts, the principal of which is that called King William's, about lat. 3° 14' N., where navigation ceases. The upper part of its course is extremely tortuous; but below lat. 5° it bends northward, and holds that direction to its embouchure. The last of the more important rapids occurs about 60 in. from the mouth of the river, and mark the limits of the tidal movement. There are many considerable islands in the river and at its mouth. The entrance is rendered dangerous by a number of sand banks, like a succession of bars lying crosswise in the channel. The whole course of the stream is perhaps 450 m., mainly through a region of great natural beauty.
The largest of the numerous tributaries of the Esse-quibo are the Rupununi, about 250 m. long; the Cuyuni, or Cuyuwini, a river of great magnitude flowing E. from the Venezuelan mountains and forming its junction near the S. part of the estuary through a mouth 1 m. wide; and the Putaro, in which is the stupendous cataract of Kaietur. (See Guiana.) Numerous excellent fish are found in the Essequibo, the most remarkable of which is the formidable peri or oma, 2 ft. long, and armed with strong teeth; also large numbers of manatees or sea cows, of gigantic size, and in most respects distinct from those of the West Indies, and electric eels. II. A part of the territory of British Guiana, now united into one county with Demerara. (See Guiana.)