Move through the water!
From the Super Mario Wiki
Aside from the conveyor belts and traps of the previous levels this stage features another element, namely water and currents. There are several pipelines in this level that produce water and hinder Wario in his quest to find the goal door. To progress, the player has to have Wario hit Switch Blocks to turn the water on or off strategically.
Hidden treasure: Hourglass
The hidden treasure of this level, Hourglass is located behind an underwater door in the area before the goal door room, but it is surrounded by currents so Wario cannot reach it. The player has to head to the goal door first, where they will find another Switch Block that turns the water out for this area. They can now return to the treasure door and obtain the treasure.
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