About five minutes in or so, someone did run out from backstage with a fire extinguisher and made an attempt at the base of the dragon. But the flames were being fed by hydraulic lines and the whole thing was in danger of coming apart from the flare-ups and small explosions as the fire spread.

There was nothing a normal fire extinguisher could do and that person was in real danger to even get near the thing. Word is they eventually let it burn out and just tried to keep it from spreading to the trees and buildings on Tom Sawyer Island.

Yes, the flames on the river are part of the show. At the start of this segment, the dragon is supposed to breathe fire on the river and set it ablaze - but the dragon fire barely worked at all at this segment because its whole system was already breaking down.