Omgosh this is so cuteee. X3 The fun the mermaid is having with the otters and the sense of movement looks great. The colours are beautiful as well. The flowey hair for the mermaid is pretty nice too; it indicates the right pace they're swimming underwater, where it seems that they're going somewhat fast, but in a more relaxed sort of way. I also love the simple decor on the bottom of the river as well. Beautiful work!
This is simple yet really pretty. It gives such a nice feeling, it does look like they're having fun, something you don't see pretty much in artworks these days with all the angst spam. Your colors and texture suit this picture perfectly.