The Great Salt Lake, located in the northern part of Utah, is the largest saltwater lake in the Western Hemisphere. It is a remnant of the prehistoric Lake Bonneville, which was once nearly as large as Lake Michigan. Because the lake has no outlet (it is endorheic), water leaves only through evaporation, leaving behind high concentrations of minerals and salts. Its salinity levels can be much higher than the ocean, making it easy for swimmers to float. While it is too salty for most fish, it supports massive populations of brine shrimp and brine flies, which in turn attract millions of migratory birds. The lake is divided by a railroad causeway; the northern half typically has higher salinity and a distinct pinkish hue due to salt-loving microbes, while the southern half is more blue-green. Currently, the lake is at record-low levels, raising concerns about toxic dust from the exposed lakebed.