See Mammoth 'Hole' Open In This Lake

Drone footage captured a mesmerising spillway that began draining water after this lake experienced record rainfall.

It may look like a portal to certain death, but the spillway in Lake Berryessa is a life-saver.

At approximately 22 meters wide and 75 meters long, the spillway acts as a drain for the Monticello Dam in Napa Valley, California. As water spirals down the spillway, it travels horizontally 610 meters before draining into nearby Putah Creek.

Created in the 1940s to supply water for irrigation and drinking, the Monticello Dam services close to 600,000 people in the area. It can hold 526 billion gallons before excess water must be drained away.

In the past couple months, the Napa region has seen record rainfalls, and the dam has become so gorged that its water capacity has reached the safe maximum limit.

MESMERIZING DRONE FOOTAGE SHOWS "WHIRLPOOL" DRAINING THIS LAKE WATCH: This circular spillway prevents Lake Berryessa in California from breaching its dam.

Kevin King, the water and power operations manager at Solano Irrigation District, helps oversee the dam's operations. He described the intended effect of the spillway as being similar to the drainage hole near the lip of a bathroom sink.

The water is flowing for the first time in 10 years at the Lake Berryessa Monticello Dam.

"As the water in the sink rises, it drains through that hole," says King. "But when it's less full, the water is stagnant."

With the current forecast, King anticipates the spillway effect will remain for the next couple of weeks.

When spillways are not properly constructed or are nonexistent, disastrous consequences can ensue. The Oroville Dam crisis that occurred earlier this month in northern California was a result of poorly constructed and ill-maintained spillways. More than 180,000 people were evacuated over fears that the dam's weir would collapse and cause major flooding for communities downstream.

Luckily for Lake Berryessa, its spillway has yet to see signs of deterioration, and it has become a popular sight-seeing spot for locals. The spillway has a number of nicknames, including the morning glory spillway and the glory hole, although King notes these monikers have become less common since the sixties.

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