Giant hole in the middle of a lake in California
Giant hole in the middle of Lake Berryessa, in California, USA.Creative Commons

Swimmers in California were shocked after discovering a mysterious giant hole in the middle of Lake Berryessa in California after a clip was shared online as onlookers questioned whether they had come across a portal to hell.

The video uploaded to Gfycat on Reddit gained a lot of popularity and has more than 150,000 views. One comment read: "Why is there a giant hole in the middle of the lake where people swim, and why is there not a rope around?" One claimed: "That right there is the portal to Hell."

The lake is over 20,000 acres (80 kmĀ²) when full and is approximately 15.5 miles (25 km) long but only 3 miles (5 km) wide.

Although the giant hole looks like some natural phenomenon, it is a man-made open bell-mouth spillway known as a 'Glory Hole'. It is 72 feet (22 m) in diameter and is used to drain the lake to stop it from overflowing. The lake can hold up to 521 gallons of water and the excess begins to flow into the spillway. The Glory Hole then works as a giant bath plug and drains the excess water.

According to The Sun, swimmer Emily Schwalek had died after he was pulled down the spillway in 1997. The 41-year-old was reportedly seen swimming towards the giant hole, spent almost 20 minutes gripping onto the edge before he dropped out of sight. Last year, for the first time in 11 years the Lake Berryessa reservoir reached full capacity.