Image imported from derpibooru
Original Description:

So in this picture Rarity and RD are a couple helping Sweetie Belle be a lifeguard. Unfortunately, Sweetie’s skills at swimming leave a lot to be desired so the couple decide to inflate all the floaties together with Sweetie and teach her swimming together. Rarity, despite having her own whistle wanted to tease her marefriend by blowing Rainbow Dash’s whistle and Dashie is only slightly annoyed as she blows up their beach ball. Sweetie is happy her sister has found the princess charming of her dreams.