A railroad causeway built in 1959 cut Utah’s Great Salt Lake into two very different lakes, ecologically speaking, as seen in this striking drone footage posted by ABC News on Wednesday. The water north of the causeway is a deep red, reflecting its highly saline chemistry.
The 20-mile rock-filed roadbed isolated the lake’s Gunnison Bay, allowing salinity levels to reach saturation levels, while the South Arm—with its regular infusion of fresh water from the Bear, Weber and Jordan rivers—has much lower salinity that rises and falls with fluctuating lake levels
ABC’s footage tracks an eastbound freight train as it approaches the causeway’s western terminal on Promontory Point, cutting a line between the contrasting waters of the lake’s North and South arms.