In his book, Embick writes: "Unrunnable for about 5 miles at all but the lowest flows, plus whatever amount of Class VI you care to try, along with easier sections lower down the river."
Embick and Roach bagged this as a first descent on May 26-28, 1990, and he's not expecting anyone to attempt a second. He rates it as being tougher than the notoriously difficult
Susitna.
The takeout is no picnic, either, involving a paddle across the treacherous Cook Inlet. You really just gotta read Embick's description of the run.
Lakes are often formed by dams, and Chakachamna Lake is no exception. However, the "dam" in this case is the aptly-named Barrier Glacier. Welcome to Alaska!