Where Did The Lake Go?

Wiki:

Lake Peigneur is located in the U.S. State of Louisiana 1.2 miles (1.9 km) north of Delcambre and 9.1 miles (14.6 km) west of New Iberia, near the northernmost tip of Vermilion Bay.

The lake was a 10-foot (3 m) deep freshwater lake popular with sportsmen until an unusual man-made disaster on November 20, 1980 changed the structure of the lake and surrounding land.

In 1980, when the disaster took place, the Diamond Crystal Salt Company operated the Jefferson Island salt mine under the lake, while a Texaco oil rig drilled down from the surface of the lake searching for petroleum. Due to a miscalculation, the 14-inch (36 cm) drill bit entered the mine, starting a remarkable chain of events which at the time turned an almost 10-foot (3.0 m) deep freshwater lake into a salt water lake with a deep hole.

It is difficult to determine exactly what occurred, as all of the evidence was destroyed or washed away in the ensuing maelstrom. The now generally accepted explanation is that a miscalculation by Texaco regarding their location resulted in the drill puncturing the roof of the third level of the mine. This created an opening in the bottom of the lake, similar to removing the drain plug from a bathtub. The lake then drained into the hole, expanding the size of that hole as the soil and salt were washed into the mine by the rushing water, filling the enormous caverns left by the removal of salt over the years. Te resultant whirlpool sucked in the drilling platform, eleven barges, many trees and 65 acres (260,000 m²) of the surrounding terrain. So much water drained into those caverns that the flow of the Delcambre Canal that usually empties the lake into Vermilion Bay was reversed, making the canal a temporary inlet. This backflow created, for a few days, the tallest waterfall ever in the state of Louisiana, at 164 feet (50 m), as the lake refilled with salt water from the Delcambre Canal and Vermilion Bay. The water downflowing into the mine caverns displaced air which erupted as compressed air and then later as 400-foot (120 m) geysers up through the mineshafts.

There were no injuries and no human lives lost in this dramatic event. All 55 employees in the mine at the time of the accident were able to escape thanks to well-planned and rehearsed evacuation drills, while the staff of the drilling rig fled the platform before it was sucked down into the new depths of the lake, and Leonce Viator, Jr. (a local fisherman) was able to drive his small boat to the shore and get out. Three dogs were reported killed, however. Days after the disaster, once the water pressure equalized, nine of the eleven sunken barges popped out of the whirlpool and refloated on the lake's surface.

The lake had salt water after the event, not as a result of water entering the salt mine, but from the salt water from the Delcambre Canal and Vermilion Bay, which are naturally salt or brackish water. The event permanently affected the ecosystem of the lake by changing the lake from freshwater to saltwater and increasing the depth of part of the lake.