You’ve seen the viral drone footage. A giant, terrifying abyss in the middle of a lake, swallowing millions of gallons of water like a drain in a bathtub. It looks like a CGI effect from a big-budget disaster movie. Honestly, when the lake berryessa glory hole starts flowing, it doesn’t even look real. It looks like the Earth just opened up a portal to another dimension.
But it's just plumbing. Massive, 1950s-era concrete plumbing.
Most people call it the Glory Hole, but engineers are a bit more formal, referring to it as a "Morning Glory Spillway." It’s basically a giant funnel built to keep the Monticello Dam from being topped when the water gets too high. When Northern California gets hit by those atmospheric rivers and the lake level hits 440 feet above sea level, the excess water has to go somewhere. Instead of spilling over the top of the dam, it drops down this 72-foot-wide concrete mouth.
It’s an engineering marvel, sure. But it’s also the subject of some pretty wild myths and one very real, very tragic history.
The Physics of the Abyss
People often describe it as a "whirlpool," but that’s technically wrong. It’s a circular weir. Water doesn't spiral down in a vortex like your kitchen sink; it flows smoothly over the lip in what scientists call laminar flow. Basically, the water slides over the edge in clean layers.
Here is the scale of what we're talking about. The mouth is 72 feet across. As the water drops, the pipe narrows down to about 28 feet. By the time that water reaches the exit point 700 feet away in Putah Creek, it’s moving. Fast. We’re talking 53 miles per hour.
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If the lake ever reached its absolute maximum design capacity—about 15.5 feet above the lip of the hole—it would swallow 362,000 gallons of water every single second.
Why is it even there?
When they built the Monticello Dam in the late 1950s, the geography of the Devil’s Hole canyon was tight. There wasn't enough room for a traditional "chute" spillway—the kind you see at Oroville or Hoover Dam that looks like a giant concrete slide. Engineers had to get creative. They decided the best way to move the water was to send it straight down through the rock.
It’s rare. There are only a handful of these in the world. Besides the one at Lake Berryessa, you’ll find another at Whiskeytown Lake near Redding, but the Berryessa one is the "celebrity" of the group because of how close it sits to the road.
The Tragedy of 1997
You can't talk about the lake berryessa glory hole without the conversation eventually turning toward safety. There’s a persistent internet rumor that people are constantly getting sucked in. That's false. In the 60-plus years the dam has existed, there has only been one recorded human fatality involving the spillway.
On March 9, 1997, a 41-year-old UC Davis graduate student named Emily Schwalen was swimming near the spillway. The lake was high, and the water was spilling over the edge. Witnesses saw her swimming toward the hole.
It’s a haunting story. She reportedly reached the edge and managed to grip the concrete lip for about 20 minutes while people on the shore watched, helpless. Eventually, she lost her grip and was pulled down into the 200-foot drop.
There’s been plenty of debate over the years about whether it was a tragic accident or something more intentional. Some relatives later suggested she might have been struggling with her mental health. Regardless of the "why," the event remains the only time a human has ever gone down the drain.
Interestingly, animals have had better luck. In 2019, a cormorant—a type of water bird—was filmed being sucked into the hole. Miraculously, it was later seen popping out the other end at the Putah Creek exit, seemingly unbothered, likely saved by its light weight and the air pockets inside the tunnel.
When Can You Actually See It?
Don't just drive out there expecting to see the show. Most of the time, the lake berryessa glory hole is just a big concrete pipe sticking out of the water, looking like a weird island.
The lake has only spilled about 25 times since the dam was completed in 1958. It's a "wet year" event.
- 2017: It spilled for the first time in over a decade, drawing thousands of tourists.
- 2019: It happened again after a series of massive storms.
- 2024: It got agonizingly close—within an inch—but never quite made the "official" spill mark for more than a few minutes.
If you’re planning a trip to see it, you need to check the water levels. The Solano County Water Agency (SCWA) monitors the lake elevation in real-time. You’re looking for a number north of 439.95 feet.
Seeing It for Yourself: A Quick Guide
If the water is high enough, it’s worth the trip. It’s free to see, and it’s one of those things that photos don't quite capture.
- The Best View: You don’t need a boat. In fact, boats are strictly banned from going anywhere near the buoy line. The best view is from the sidewalk along Highway 128, right next to the Monticello Dam.
- Parking: There’s a small turnout right at the dam. It gets crowded fast when the hole is flowing. If you can’t find a spot, keep driving—there are other pullouts further up the road, though you’ll have to walk back.
- Drones: People love flying drones over the hole. If you do this, be respectful of others and follow FAA rules. The wind at the dam can be surprisingly strong, and many a drone has ended up at the bottom of the lake after a sudden gust.
The Skateboarder Legend
During the drought years, the lake level drops so low that the exit tunnel at the bottom (on the Putah Creek side) becomes completely dry. Local skateboarders and urban explorers have been known to hike into the tunnel to use the curved concrete as a massive, 28-foot-wide halfpipe. It’s technically trespassing and incredibly dangerous if there’s any chance of rain, but the graffiti inside tells a long history of "dry season" visitors.
Actionable Insights for Your Visit
If you’re heading out to Lake Berryessa, whether the spillway is flowing or not, here’s how to do it right:
- Check the Level First: Visit the SCWA website or the Lake Berryessa News page before you leave. If the level is below 438 feet, the hole will just be a dry concrete ring.
- Avoid Weekends: If the hole is active, Highway 128 becomes a parking lot on Saturdays. Go on a Tuesday morning if you can.
- Bring Binoculars: You can see the water rushing over the lip from the road, but binoculars let you see the incredible texture of the water as it breaks over the concrete.
- Respect the Buoys: Seriously. The current near the lip is deceptive. Even if you're a strong swimmer, the pull of thousands of tons of water is not something you win against.
The lake berryessa glory hole is a reminder of how we tried to tame the California wilderness with concrete and math. It’s beautiful, it’s a little bit scary, and it’s a perfect example of 1950s "big infrastructure" that still works exactly as intended today. Just stay behind the fence and enjoy the view.