English: When viewed from space, the two-toned waters of Utah's Great Salt Lake seem to be surrounded by a sinuous silhouette of salt set on a backdrop of expansive desert tan. On August 1, 2017, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite acquired a striking true-color image of the Great Salt Lake shining under late-summer skies.

The Great Salt Lake claims the title of the largest lake west of the Mississippi River, but it is only a tiny remnant of a giant ice-aged body of water. Prehistoric Lake Bonneville stretched over more than 20,000 square miles (51,800 sq. km), flooding parts of Utah, Nevada, and Idaho. Today the Great Salt Lake measures about 75 miles (120 km) long and 35 miles (56 km) wide, with a surface area of about 2,600 sq. miles (6,700 sq. km). The maximum depth is only 33 feet (10 m), but water levels in the lake shift with regional precipitation. After a series of wet years the shorelines can expand as much as 15 feet (4.5 m).

The Great Salt Lake is a “terminal basin”, which means the water that pours into the lake from four major rivers and several streams has no outlet other than evaporation. Evaporation and the relatively shallow water levels has led to high salinity (dissolved salt content) in the lake, but the salinity is not uniform. The north arm of the lake typically has twice the salinity of the rest of the lake due to impoundment of water by a railroad causeway that crosses the lake from east to west. The causeway restricts water flow, and the separation has led to a striking division in the types of algae and bacteria found in the north and south arms of the lake. North of the causeway, the red algae Dunaliella salina and the bacterial species Halobacterium produce a pronounced reddish cast to the water, whereas south of the causeway, the water color is dominated by green algae such as Dunaliella viridis. Although the briny waters are too salty to support fish, brine shrimp and brine flies flourish in the ecosystem. The lake and surrounding wetlands are also a major stopover point for migratory birds including avocets, stilts, and plovers.