Major U.S. Watersheds

Watersheds are like big bowls, separated and defined by an area of land, a ridge, or a divide that drains rainwater runoff in that basin.

There are 78 major river basins, or watersheds, in the lower 48 states.

As water moves from the sky to the land to the ocean it travels overland and through the ground in bounded basins called watersheds.

Temperature and rain patterns, underlying rock types, and topography (mountainous, hilly, flat) influence the structure of these watersheds and help to define the specific types of habitats available along the river continuum in each watershed.

As one of the 78 major watersheds in the contiguous U.S., the Delaware River watershed (marked in red) supplies water to about 5% of the nation’s population. The Delaware River is the longest undammed river east of the Mississippi.

View the Delaware River watershed »