The surface level of Great Salt Lake, Utah, fluctuates continuously, primarily in response to climatic factors. During 1847-1982 the lake surface fluctuated between a low of about 4,191 feet and a high of about 4,212 feet above sea level but showed no net change. From September 18, 1982, to June 30, 1983, however, the lake rose 5.2 feet-from about 4,200 to about 4,205 feet above sea level-which is the greatest seasonal rise ever recorded. That rise resulted from considerably greater than average rainfall in 1982, greater than average snowfall during the autumn of 1982 through the spring of 1983, and unseasonably cool weather during that spring.

Man's activities have had a lesser, but still important effect on the lake level. The lake surface would have been about 5 feet higher in 1983 had there been no consumptive use of water owing to man's activities in the lake basin since 1847. The lake has been divided into two parts by a railroad causeway since 1959. The causeway restricts natural circulation, resulting in a difference of salinity and surface level of the lake across the causeway. The difference in surface level between the two parts of the lake varies both seasonally and annually and was as much as 3.25 feet in 1983.

The water budget for the Great Salt Lake can be expressed as:

Inflow = Outflow ± Storage change

The average annual inflow for 1931-76 was about 2.9 million acre-feet-about 1.9 million acre-feet from surface water, about 900,000 acre-feet from direct precipitation, and about 75,000 acre-feet from ground water. The average annual outflow for the same period, all by evaporation, also was about 2.9 million acre-feet. There was no net change in storage during the period.

The famed buoyancy of the brine in Great Salt Lake results from a dissolved-mineral content of almost 5 billion tons. More than 2 million additional tons have been added to the lake annually in recent years. The major dissolved ions in the brine are chloride, sulfate, sodium, magnesium, and potassium.

Prior to completion of the railroad causeway, the salinity of the brine varied inversely with the lake level. Since the causeway divided the lake into two parts, the salinity of the brine in the north part has been relatively constant at or close to saturation. The salinity of the brine in the south part has 1 continued to change inversely with the lake level, but the salinity has been less than it would have been without the causeway.