Copco 1, the oldest of the three remaining dams on the Klamath River, was breached Tuesday.

Crews blasted away a plug in Copco’s adit, a 10-foot-diameter tunnel that was drilled at the base of the dam last summer.

Ren Brownell, spokeswoman for Klamath River Renewal Corporation, which is coordinating the dams’ removal, said crews went about 100 feet into the dam and left a 12-foot concrete plug at its upstream end. A steel pipe was installed on its exterior and covered with concrete and a large rock.

Earlier this month, openings were created at the two other hydroelectric dams — Iron Gate and John C. Boyle — as part of drawing down water from the reservoirs behind the dams. A fourth dam, Copco 2, was removed last year.

“They’re all initiated,” Brownell said of the drawdown phase. Depending on water runoff, the reservoirs could all be completely drained by mid to late February. If heavy rain and snow fall, the drawdown could extend to early spring, she said.

A video of the explosion shows a cascade of brown, sediment-filled water gushing through the opening. Brownell said that, as the plug was removed, water sprayed high into the air. No one was allowed on-site because of the force of the blast.

Crews from the Yurok Tribe Fisheries Department’s revegetation crew recently began sowing native plant seeds in the newly exposed soil to take advantage of the soil’s moisture and to prevent invasive weeds from taking root. Restoration work will also be done at the former J.C. Boyle Reservoir, commonly known as Topsy, and at Copco 1.

While the path of the Klamath has resumed, areas by the reservoirs that were water-covered have turned into mud flats. It’s expected to take several years to restore areas exposed by the removal of the reservoirs. Extensive revegetation efforts have already started near the Iron Gate Dam.

The Yurok Tribe wrote in a social media post:

“By next year, the Klamath will flow free for the first time in a century. The seeds put in the ground this winter will germinate and grow into plants.

“As the flora matures, the 38-mile-long reservoir reach will provide habitat for a myriad of native fish and wildlife. What was previously a dead zone will be brought back to life.”

Since Monday, the Yurok crew has planted over 10,000 white oak acorns and scattered hundreds of pounds of special blend of 20 different native grasses, herbs and flowering plants, ranging from golden California poppies to blue wild rye, according to the tribe’s post.