1963 -- 1972 -- 1987 -- Map
The Great Salt Lake is a terminal lake, with no outlet rivers running to the ocean. Since water leaves the lake only through evaporation, it leaves behind its dissolved minerals, making the lake up to 8 times as salty as sea water.
The lack of outlets also means the lake responds dramatically to change in inflow. Rainy weather beginning in 1982 brought the highest levels in recorded history, peaking in June 1986 and March-April 1987. The lake is shallow for its size-- about 70 miles long and 30 miles wide, but only about 40 feet deep. Because the lake basin is so shallowly sloped, extra inflow to the lake makes it rise only slowly, but any rise means a large increase in area. Highways, causeways, and parts of Salt Lake City were flooded or threatened in the 1980s, costing millions of dollars.
But unlike the trestle, which allowed water to circulate freely underneath for 12 miles, the causeway had only two 15-foot culverts. The causeway rock-fill was only semipermeable, so it reduced north- south flow, splitting the lake into two parts. The south part receives most of the lake's inflow from rivers, so it became higher than the north part. The northern part also became saltier, which in turn caused different types of algae and bacteria to grow there, which in turn made the north part look pink, while the south part was bluer. Depending on your monitor, you should see this subtle difference in the 1972 Landsat image (in this image, reflectance in the visible-red range is represented by green).
By 1 July 1984, after two years of above-normal precipitation, the south part of the lake was 3.7 feet higher than the north, the highest difference it would ever reach. By 3 August of that year, a 300-foot section of the causeway was replaced by a low bridge, allowing water to flow underneath. Within 2 months the difference between the south and north fell to 0.75 feet, and within a year it was only 0.5 feet. Although this was done as a flood-control measure, it also had the effect of reducing the difference in salt concentration. By 1987, the north-south difference visible in Landsat images was reduced.
In the first year, about 1.5 million acre-feet of water was pumped into the evaporation basin (an acre-foot is a volume that would cover one acre with one foot of water). A dike was built at the southeast end of the basin to control the basin's water level and let salt-rich water flow back into the lake--so that if the level of the basin rose high enough, some water would travel all the way around the Newfoundland Mountains and back into the lake. Over the course of the project an estimated 264,000-283,000 acre-feet of water actually did so.