"Ask them?" Morgana's still adjusting to purple water. She's not entirely sure the locals are good to meet yet.

On the other hand, the Doctor wants to ask where everyone is. More so, he's so curious he's tracking them down, hence there is only one conclusion.

Moving a a bit faster through the water than him -- the splash doesn't bother her, water dries -- to catch up.

"Doctor," she says when she does reach him, "What is wrong here?"

This is the Doctor. She automatically assumes something's gone wrong.