A continental divide is a naturally occurring boundary or ridge separating a continent’s river systems. Each river system feeds into a distinct ocean basin, bay, or sea.

Continental divides are broad, continent-wide example of drainage divides, sometimes just called divides. Divides are boundaries that separate drainage basins or watersheds of all sizes. Drainage divides, regardless of scale, occur in raised terrain such as mountain ranges or hills.

Generally, precipitation that falls on one side of the divide will flow to one basin and precipitation that falls on the other side will flow to another basin. 

In some cases, water runs toward an endorheic basin, such as a saline lake or salt flat. Endorheic basins, which do not connect to an ocean or other large body of water, usually occur in desert areas. Much of the Sahara Desert in Africa, for example, is an endorheic basin. This means that rivers and streams that flow into Lake Chad, on the edge of the Sahara, have no outlet to either the Mediterranean Sea or the Atlantic or Indian Oceans.

Continental divides are found on every continent. Continents that are bordered by more than two bodies of water may have more than one continental divide. For example, North America has between three and five divides. Scientists have not yet agreed on a specific number because the exact border between ocean basins is not universally accepted.

Some continental divides span multiple continents. For example, the Continental Divide of the Americas, or the Great Divide, runs through much of North and South America. It separates the water that runs toward the Pacific Ocean from the water that runs toward the Atlantic and Arctic Oceans and the Gulf of Mexico. This divide runs from Cape Prince of Wales in western Alaska, through the Rocky Mountains of western Canada and the continental United States, then through the Sierra Madre Occidental mountains in Mexico, through Central America and along the Andes Mountains of South America.