It's called a "Glory Hole."
For the first time in 10 years, Lake Berryessa's Glory Hole is overflowing with water. As of Tuesday, the water level was 1.3 feet above the spillway.
The unusual drain—which was designed to function just like a bathtub waterway would—helps maintain storm overflow in Northern California. It has attracted people from around the world with its portal-like design.
A series of storms helped push the spillway over its limit, and visitors were warned to take extra care in the area, as the abundance of moisture makes it easier for land and mudslides to occur.
But the overflow also created a spectacular sight of swirling water, and YouTuber Evan Kilkus caught it all on video from his drone, and then shared the footage with Storyful.
The rainfall was expected to last until Wednesday, meaning this overflow probably won't stick around very long. Check out drone footage of the spillway above.