Lake Peigneur is a brackish lake in the U.S. state of Louisiana, 1.2 miles (1.9 kilometers) north of Delcambre and 9.1 mi (14.6 km) west of New Iberia, near the northernmost tip of Vermilion Bay. With a maximum depth of 200 feet (60 meters), it is the deepest lake in Louisiana. Its name comes from the French word "peigneur", meaning "one who combs."

Previously, it had been a 10-foot-deep (3 m) freshwater lake, popular for recreation, until human activity caused an unusual disaster on November 20, 1980, that changed its structure and the surrounding land.

In petroleum geology, the formation of a salt dome often pushes terrain upward from the surrounding land, while also creating a subterranean salt dome trap, holding petroleum deposits. On Thursday, November 20, 1980, the drill assembly of a Texaco contracted oil rig, just offshore of the salt dome-caused Jefferson Island (itself in the east southeast section of Lake Peigneur), pierced an inactive third level of the Diamond Crystal Salt Company salt mine. The hole produced a vortex that drained the lake into the mine, filling the enormous caverns that had been left by the removal of salt.

The mine, in operation since 1919, was made up of several levels up to 1,500 feet (460 m) below the surface. Each tunnel was about 100 by 80 feet (30 m × 24 m). Pillars of salt had been left in place to support the ceiling at each level. The pillars were dissolved by the encroaching fresh water and caused the mine tunnels to collapse.

The resultant sinkhole swallowed the drilling platform, eleven barges holding supplies for the drilling operation, a tugboat, many trees, and 65 acres (26 hectares) of the surrounding terrain, including much of Jefferson Island. So much water drained into the caverns that the flow of the Delcambre Canal that usually empties the lake into Vermilion Bay was reversed, causing salt water from the Gulf of Mexico to flow into what was now a dry lakebed. This backflow created for a few days the tallest waterfall ever in the state of Louisiana, at 164 ft (50 m), as the lake refilled with salty water from the Delcambre Canal and Vermilion Bay. Air displaced by water flowing into the mine caverns erupted through the mineshafts as compressed air and then later as 400-foot (120 m) geysers.

Although there were no human deaths, three dogs were reported killed. All 55 employees in the mine at the time of the accident escaped, with six employees later given awards by Diamond Crystal for heroism. Their successful evacuation was thanks to the mine's electrician who noticed a torrent of water and sounded the alarm, as well as the employees' discipline and training making their escape via the only elevator in an orderly fashion. The crew of seven on the drilling rig fled the platform shortly before it collapsed into the new depths of the lake. A fisherman who was on the lake at the time piloted his small boat to shore and escaped. 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.

On the date of the disaster, the oil rig was conducting exploratory drilling in the lake alongside a salt dome under the water, that contained a salt mine.

The rig's 14-inch (36 cm) drill assembly had become stuck at 1,228 feet (374 m) two-and-a-half hours before the drilling rig began to tilt.

The drill assembly punctured the salt mine beneath the lake, and the water entered the mine. Over the course of several hours, the fresh lake water dissolved the salt and enlarged the hole, causing the lake to drain into the mine.

The Mine Safety and Health Administration was unable to determine blame because they could not determine whether Texaco was drilling in the wrong place or if the mine's maps were inaccurate.

Evidence that could have confirmed the cause was washed away in the maelstrom. Engineers from Texaco and Diamond Crystal worked together after the fact and pinpointed the likely location of the hole within a mined out portion of the 1300-foot level of the mine.

In 1983, Texaco and the drilling contractor Wilson Brothers paid US$32 million (equivalent to $98 million in 2023) to Diamond Crystal, while Texaco, Wilson Brothers and Diamond Crystal also paid a total of $12.8 million (equivalent to $39.2 million in 2023) to the Live Oak Gardens botanical garden and plant nursery, in out-of-court settlements to compensate for the damage caused. The Mine Safety and Health Administration released a report on the disaster in August 1981 which exhaustively documented the event but stopped short of identifying an official reason for the disaster. The mine was finally closed in December 1986.

Since 1994, AGL Resources has used Lake Peigneur's underlying salt dome as a storage and hub facility for pressurized natural gas. There was concern from local residents in 2009 over the safety of storing the gas under the lake and nearby drilling operations.

• Bayou Corne sinkhole
• Döda fallet
• Lake Beloye (Nizhny Novgorod Oblast)
• List of sinkholes of the United States
• Rylands v Fletcher

• Lake Peigneur: The biggest sinkhole ever created (archived)
• Oil Driller Breaches Salt Mine Under Louisana [sic] Lake on YouTube
• Endangered Earth - Sinkholes Assorted
• Warren, John K. (2006). Evaporites: Sediments, Resources, and Hydrocarbons. Berlin; New York: Springer Publishing. pp. 928–930. ISBN 9783540260110. Retrieved 2020-02-04. Contains a description of the event, with a focus on the geology of the region.
• Mine-mouth geyser problem, Chemical Engineering Education, an in-depth discussion of how the inrush of water could have created a powerful geyser
• Gold, Michael (November 1981). "Who Pulled the Plug on Lake Peigneur?". Science 81. pp. 56–63.
• The podcast Eclipsed has a two-part episode about Lake Peigneur. Part 1 Part 2