Vortex

"Monticello Dam is a 304-foot (93 m) high concrete arch dam in Napa County, California, United States constructed between 1953 and 1957. The dam impounded Putah Creek to create Lake Berryessa in the Vaca Mountains.
Lake Berryessa is currently the seventh largest man-made lake in California. Water from the reservoir primarily supplies agriculture in the Sacramento Valley downstream. The dam is noted for its classic, uncontrolled morning-glory type spillway. The diameter at the lip is 72 ft (22 m). Locally, the spillway is also known as 'The Glory Hole.' The dam's morning glory type spillway, known as the Glory Hole, is 72 feet (22 m) in diameter at lake level and narrows down to about 28 feet (8.5 m) at the exit. At the lake's peak level the spillway can drain 48,400 cubic feet per second (1,370 m3/s), which occurs when the lake level rises to 15.5 feet (4.7 m) above the level of the funnel."

My photo does not do this justice. It was a surprise along to the drive to a meeting and amazing to see.