"The Deep End"

Mabel befriends a cute merman trapped in the deep end of the public pool, and is determined to return him to his family in the ocean – even though that means her whirlwind of a romance will come to an end. Meanwhile, Dipper learns that Wendy is a lifeguard at the pool, so he decides that the best way to spend time with her is to volunteer. Elsewhere, it's all out war for the best lawn chair at the pool between Stan and Gideon.