The spell wasn't working! Why wasn't it working? The useless wand in her hand, Kiri watched, horror-struck, as the teacher (he looked like... Professor Lawson?), still trying his best to keep the house elves away from the water, spiralled closer and closer. When she realised what was going to happen, it was too late.
They crashed into her.
The algae-coated steps didn't offer any grip, and she slipped, shouting in surprise, her madly flailing arms reaching neither Clifford nor one of the other students. She nearly lost her wand again as she stumbled forward, but pure instinct made her hold on to it.

She thought she'd managed to escape the water, but here it was again, and this time it wasn't just her shoes that were getting wet. For a moment, Kiri's entire body was submerged, slimy pieces of water plants touching her face for a moment before being pulled down the corridor by the tide. The water stung in her eyes. All sense of direction had been lost instantly.
When a strong arm gripped her around the waist, the force pushed all remaining air out of her. She swallowed a lungful of the icy, metallic-tasting water, but then Professor Lawson managed to get her head above the surface again. Kiri gagged and spat, all the while pirouetting away from the steps.

Something heavy dropped onto her shoulders, pulling her hair. In her panic, Kiri thought for a moment that the water had somehow evolved an... arm of sorts to push her down, but then a high-pitched squeal forced its way into her ear. One of the house elves had scrambled onto her shoulders. She tried desperately to stay afloat, especially now that she had the creature to take care of as well.
Then Kiri's head rammed into the wall. There was a moment of excruciating pain that seemed to fill her vision with blinding white light, and then she was out cold.