California has done it again. For the first time in six years, the famous “glory hole” spillway at Lake Berryessa is back in action, according to CBS News.
No innuendo here—this refers to the uniquely designed spillway at the North Bay reservoir, next to the Monticello Dam.
“It’s called a glory hole spillway. That’s the official engineering term, and we just shortened it to glory hole,” local historian, scientist, and journalist Peter Kilkus told CBS. “Some find it beautiful, while others think it looks terrifying.”
The full name isn’t less attention-grabbing: the Morning Glory Hole spillway.
So, what exactly is it? Essentially, it’s a massive, 70-foot-wide drain—also known as a “passive spillway.”
When the lake’s water level exceeds 440 feet, the excess water flows into the drain, funneling through an underground discharge channel.
When active, the spillway creates a surreal sight, almost like a portal to another dimension—or a glitch in reality itself. Seeing a hole in the middle of a lake feels unnatural, yet mesmerizing.
“It’s a huge tourist attraction,” said Kilkus, who runs Lake Berryessa News. “On busy weekends, parking here is nearly impossible.”
The spillway is rarely in use. Before this, it last saw overflow in 2019 and 2017, and before that, it had been inactive since 2005, according to Chris Lee, general manager of the Solano County Water Agency.
The history of the spillway is deeply connected to the lake itself. Lake Berryessa was formed in 1957 when the Monticello Dam was built, submerging a small community in the process.
Due to the dam’s location in a narrow canyon, there wasn’t enough space for a traditional spillway beside it.
Instead, engineers designed a vertical drain in the lake that drops water 200 feet before making a sharp turn and releasing it into Putah Creek.
“This design is quite rare,” Kilkus noted. “There are only two in California and a few in Europe, but they’re uncommon worldwide.”
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