Over a century ago, Shadowcrest Island was home to ordinary humans with ordinary lives. They had made a life on the island after a huge shipwreck which left them stranded. They were never found, so they managed to survive on their own. After 50 years, a witch found the island and cursed every single human to the sea. She turned the females into mermaids and the men into mermen, giving them a mermaid tail and underwater abilities to survive. Another part of the curse was that if they stepped on human land, they would be banished to a mermaid and merman prison called Silver Creek, run by an evil merman.
It's been 99 years, and the island eventually got discovered. Now, other humans live on the island because of the want for a quiet and peaceful life. They don't know about the curse 100 years ago, and don't know that the merpeople exist. The merpeople don't even know about the humans, as they think it is still deserted. However, they don't know for sure, because if they go up there they will be banished, and they are quite accustomed to their life now.
It's been 99 years, and the island eventually got discovered. Now, other humans live on the island because of the want for a quiet and peaceful life. They don't know about the curse 100 years ago, and don't know that the merpeople exist. The merpeople don't even know about the humans, as they think it is still deserted. However, they don't know for sure, because if they go up there they will be banished, and they are quite accustomed to their life now.