A flooded chamber in the mines

The mines' east chamber is under water, and its water connects to nothing Dizzy can reach from the mines.
Nudge 1Where to look
Water comes from somewhere above: Silver Stream runs over this part of the mines.
What you needOther problems to solve first
Solve these first (each opens its own page, no answers on the way):
Show the solutionThe whole answer, with a video
It's entered from above, through the pit under Silver Stream's old bridge (Under Silver Stream), with the aqua lung and the flippers. Inside are the pair of brass cymbals and three stars. Swim out west into the mines' upper corridor.