PI-39 Commonly Asked Questions About Utah's Great Salt Lake and Ancient Lake Bonneville

Areal extent, elevation, volume, and maximum depth of Great Salt Lake at historic high, average, and historic low-water levels.

How big and how deep is the lake, and why does it change in size?

Great Salt Lake averages approximately 75 miles long by 35 miles wide at a surface elevation of about 4,200 feet.  At this elevation, the lake covers an area of 1,034,000 acres, and has a maximum depth of about 33 feet.

It is reported to be the 33rd largest lake in the world, and the largest fresh or saltwater lake in the United States after the Great Lakes.  Its size and depth, however, vary both seasonally and over the long term.  The magnitude of these changes depends on the balance between the total amount of water that enters the lake and that which leaves.

On average, the lake level fluctuates one to two feet annually, rising to its highest level during May through July (following the melting of the mountain snowpack) and dropping to its lowest point during October through November (after the hot summer months). 

In historical time (1847 to present), fluctuations of the lake level have varied over a range of 20 feet from a low of 4,191.35 feet in 1963 to a high of 4,211.85 feet in 1986-1987.  The historical average elevation of the lake is about 4,200 feet.

Because of the very shallow nature of the lake, even modest changes in its elevation result in relatively large changes in the lake's area and volume.  The accompanying map shows the high, average, and low elevations of the lake and pertinent information for each of these elevations.

Historical elevations (in feet above mean sea level) of the southern arm of the Great Salt Lake (at its highest point for the year), 1847-1994 (USGS provisional lake records).