The Great Salt Lake is drying up and shrinking. Both nature and man have a hand in the change.

The Great Salt Lake is largest water body in the United States after the Great Lakes. It is a terminal basin, which means the water that pours into the lake from rivers and streams has no outlet other than evaporation. This allows salts and minerals to concentrate in the lake such that it is three to five times saltier than the ocean. And yet this briny lake is a haven for more than 250 species of migratory birds who feast on the brine shrimp and flies that thrive there.

But now the millions of birds and shrimp—and the people who harvest the shrimp and extract salts and recreational fun from the lake—are faced with a problem. For more than 150 years, humans have been taking more water out of the Salt Lake watershed than is flowing into it. They are now diverting about 40 percent of the river water (which would normally fill the lake) and using it for farming, industry, and human consumption. In October 2016, the Great Salt Lake reached its lowest recorded level: 1277.5 meters (4,191.2 feet), averaged between the lake's north and south arms.

Five years of drought in the American West have contributed to the recent drop in the water line, as have higher-than-normal temperatures. But the region has seen dry cycles before, and according to scientists, there has not been a significant long-term change in precipitation in the basin. Nonetheless, the volume of water in Great Salt Lake has shrunk by 48 percent and the lake level has fallen 3.4 meters (11 feet) since 1847.

These two Landsat satellite images show recent changes in the Farmington Bay basin of Great Salt Lake. The Thematic Mapper on Landsat 5 acquired the first image on September 11, 2011; the second image was captured by the Operational Land Imager (OLI) on Landsat 8 on September 20, 2016. According to scientists’ estimates, more than three-quarters of the lake bed is now exposed in Farmington Bay. Salt Lake City (lower right) and its northern suburbs stretch around the east side of the lake.

“Farmington Bay has been nearly desiccated as the result of the combined effects of drought and water withdrawals from the rivers feeding the lake,” said Wayne Wurtsbaugh, who studies watershed sciences at Utah State University. “Farmington Bay is an immensely important feeding area for migratory shorebirds and waterfowl. Even at the low level we have now, it is still important, but the greatly reduced size has diminished its value.”

In a white paper released in February 2016, Wurtsbaugh and colleagues described the impact of water development on the Great Salt Lake. Using hydrogeologic data and models, the team found that river flow into the basin—from the Bear, Jordan, and Weber rivers—has been reduced 39 percent since the middle of the 19th century. Water that once spread across roughly 4100 square kilometers (1,600 square miles) now covers just 2700 square kilometers (1,050 square miles).

“The solution to the water issue is greater conservation, particularly for agricultural irrigation,” said Wurtsbaugh. The state has been promoting water conservation for urban and suburban areas, but this is only about 8 percent of water use. And while per person water use is down by 18 percent, those gains are offset by a growing population that is increasing overall water use.

The hardest work lies in convincing farmers to do more with less, as approximately 63 percent of the water usage goes to agriculture. Researchers and conservationists are also concerned about future plans for development along Bear River, the largest tributary flowing to the lake.

The loss of water in Great Salt Lake has led to more and larger dust storms in the area, while making it harder for companies to get the water they need for extracting salt and other minerals, a key piece of the local economy. Marinas and other water recreation operations are also struggling with the moving shoreline.

“A wildcard for the fate of the lake is what global climate change may do to the basin,” said Wurtsbaugh. “Warmer air temperatures are projected to lower runoff, but our data shown in the white paper suggests there haven't been climate change effects on the runoff yet.”

NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Caption by Michael Carlowicz.