Found you
The water began to slash and bubble in the distance scaring several of the youngins but piquing the interest of the older generation that went even closer to see it first hand.
And right in front of everyone's eyes a gigantic seashell slowly emerged from the depths of the ocean. It was at least 300 meters in size from what they could see, probably even more if the submerged part was taken into account.
The upper portion of the shell raised just a smidgen and the merman walked out of it. He actually walked out on the water as if it was solid ground stopping just a couple of meters away.
"Now then, everyone! Please form a line and follow in my footsteps."
People were hesitant at first until an old man with a long flowing white beard jumped into the water ended up standing on top of it.
"Hahaha, you must teach me your water magic friend!"
"That will be extra sir," the merman responded without turning back.