How does an entire lake disappear overnight? This disturbing event is occurring around the world with greater frequency. The latest happened in the Patagonia region near the southern end of Chile. Lake Riesco, a 1400 hectare (14 square km/5.4 square mile) body of water popular with fishing enthusiasts and vacationers, is gone and no one can explain why.

Local media showed before-and-after photographs of the area on May 30th, 2016, using words like “shocking” and “desiccated” to describe the scene at what was once Lake Riesco (Lago Riesco) in the valley of the river Blanco in the Aysén province, 27 km (16 miles) from the provincial capital city of Puerto Aysen. Before its demise, Lago Riesco had a maximum depth of 130 meters (425 feet) and an average depth of 72 meters (236 feet). After its demise, it’s dry. Why?

Reports on May 30th say “still no official information on the case.” Volcanoes in the area were “stable” with no unusual activities. Unofficially, speculation points to a few possible causes. One side of Lake Riesco lies on the Liquiñe-Ofqui geological fault – a major fault line which runs for 1200 km through southern Chile. The fault regularly triggers earthquakes, but no significant seismic activity was reported prior to the disappearance of Lake Riesco. There are reportedly no visible holes or crevices where the water could have gone.

Another less plausible explanation is the drought caused by El Nino which has affected the area. Average rainfall in the lake region this year is only 34% of normal annual precipitation. While this may explain the lake being at lower levels and exposing new stretches of beaches, a gradual decline due to climate doesn’t suddenly become an overnight disappearance. Despite that, this is the preliminary explanation given by Marcio Villouta Alvarado, the Ministerial Regional Secretary of Public Works.

A large lake vanishes overnight without seismic warnings, loud noises, sudden and drastic changes in weather or other logical explanations for this strange event deep in the beautiful forests of Patagonia. What else could have caused it?

Local residents, boaters, swimmers and birds wait for an explanation. It’s too late for the fish.