Georgetown, Essequibo River Mouth, Guyana August 1985 The mouth of the sediment-laden Essequibo River is visible in this west-looking view. The Essequibo River, the longest river in Guyana at 600 miles (995 km) long, rises in the Guiana Highlands near the Brazilian border. The river flows northward to the Atlantic Ocean and there are rapids and waterfalls along most of its course. East of the Essequibo is the smaller Demerara River (near center of image), which is 200 miles (320 km) long and rises in the Guiana Highlands of eastern Guyana. The river is navigable for ocean-going vessels inland to the port city of Mackenzie (not visible on image), an important exporting center for bauxite and kaolin. Georgetown, the capital city of Guyana, is on the east bank of the Demerara River at the Atlantic seacoast