BOULDER, Colo. (KDVR) — Denver Water announced that recreation at Gross Reservoir was closed until further notice.

According to Denver Water, emergency responders worked on an accident that took place early Saturday morning at 12:30 a.m. during the Gross Reservoir Expansion Project.

When responders arrived at the project site, they were told a worker had seen the headlights of a vehicle rolling down an embankment near the dam.

Colorado State Patrol believes a person driving a dump truck in the area may have been too close to the reservoir and rolled in. The truck was hauling 7,000 pounds of rock.

The driver was lost in the reservoir and the truck was completely submerged.

Upon arrival, first responders requested the Northern Colorado Med Evac helicopter to fly over the area with a spotlight. A dive team then went in to locate the driver, however, they proved unsuccessful.

After a period of time, the search transitioned from rescue to recovery mode. Sonar operations were conducted to determine the depth of the truck in the water. The scan showed the truck was up to 43 feet at the deepest point.

Divers were able to access the cab of the truck and locate the driver.

The driver was pronounced dead, and the identity will be announced by the Boulder County Coroner’s Office.

The reservoir was closed to on-water recreation, camping, hiking and picnicking.

The expansion project was given the green light in 2020 in an effort to raise the dam’s height by 131 feet to 471 feet. When the project is completed, the dam will hold an additional 77,000 acre-feet of water, which is equivalent to more than 25 billion gallons of water.

The project is expected to be completed in 2025.