This picture is based on how Tenon was first introduced to Applejack. He was commissioned to building a very large wooden tub, more of a pool, presumably for collecting and storing rainwater. As he came back for checking up on the work he'd done and making sure everything was sealing up and holding properly, he found out the pool had another use:
Applejack had already been to see the sea horses, and still retained a pendant from Queen Nova allowing her to switch to her seahorse form. The pool allowed her to enjoy some private seashorse time without potentially being seen at a local lake or pond.
Of course, as she's swimming... she's not wearing clothes. This led to a hurried offer of Tenon's shirt, while they talked on the pool edge, and things calmed down considerably as they shared a cider together.

Picture is by the awesome  baroncoon.