GREAT SALT LAKE

Great Salt Lake is the largest natural lake west of the Mississippi River. The lake is a remnant of prehistoric Lake Bonneville, which covered more than 20,000 square miles during the Ice Age. Four distinct shorelines of Ancient Lake Bonneville may be seen from Antelope Island and include Bonneville, Provo, Stansbury and Gilbert.

Great Salt Lake is currently 75 miles long by 28 miles wide, covering 1,700 square miles. At this level, maximum depth is about 33 feet. Size and depth of the lake vary greatly with seasonal evaporation and precipitation.

Water flows into the lake from four river drainages, carrying 2.2 million tons of minerals into the lake each year. Great Salt Lake does not have an outlet; water leaves only through evaporation. Because of this, high concentrations of minerals are left behind. Salinity levels range between 4 and 28 percent compared to the ocean at 3 percent.

Salinity is too high to support fish and most other aquatic species, however, brine shrimp, brine flies and several types of algae thrive in the lake. Brine shrimp and brine flies tolerate the high salt content and feed on algae. Brine flies and brine shrimp are the primary s=food source for millions of migrating birds.

The mineral industry extracts about 2 million tons of salt from the lake each year. Millions of pounds of brine shrimp eggs are harvested commercially and sold as prawn and fish food.

Oolitic sand is a unique feature of Great Salt Lake. These round grains of sand are formed when mineral grains or brine shrimp fecal pellets are coated by concentric layers of aragonite, a form of calcium carbonate. This is similar to how pearls are formed. Calcium is abundant in Great Salt Lake because of nearby limestone.

Nearly 80 percent of Utah's wetlands surround Great Salt Lake, making its ecosystem one of the most important resources in North America for migratory and nesting birds. The are hosts 250 bird species each year, which represents a significant part of the 6 to 9 million migratory birds passing through the Pacific Flyway. The lake and its marshes provide a resting, nesting and staging area for birds, as well as an abundance of food in the form of brine shrimp and brine flies.

There are eight major islands in the Great Salt Lake– Antelope, Stansbury, Fremont, Carrington, Gunnison, Dolphin, Bird (Hat), and Badger. Smaller rock outcroppings appear at lower lake levels. Gunnison, Bird, Egg, and White Rock islands are bird rookeries and public access is not allowed.