Suriname is composed of thick forests, unexplored mountains, and swampy plains. Approximately 80% of the territory is classified as tropical rain forest. Several geologically old rivers, including the Maroni in the east and the Courantyne, flow northward to the Atlantic Ocean from the southern highlands near the Brazilian border; there, numerous rapids and waterfalls bar boat passage.
The coastal plain is flat and sometimes as much as 1.5 m (5 ft) below sea level, necessitating a system of sea defenses. The soils of the coastal plain are relatively fertile. A forest belt, 48–72 km (30–45 mi) wide, lies to the south, interspersed with grassy savannas. Farther south are dense forest and higher ground.