Holy carp! It’s a miracle the boat didn’t drift sideways against the spillover. It would have very likely been rolled over the edge of the dam by the flow.
Articles says by that time, they were in full reverse but the motor wasn’t powerful enough to pull them away but it did maintain their position at least until help arrived. Luckily someone saw them pretty quick. They had an electric outboard and who knows how long the battery would have held up.