Hello M3tztl1,
As promised, I just added swimming animations to this assetpack. You can download v1.2 to access them.
I went just with 2 animations for now, please let me know if they work for your needs or if you need anything else. Theorethically it should be possible to use the same loop for swimming up and down - many games do it like that (I referenced Donkey Kong Country 2's system for the ones I added). You can leave me a comment here or also send me gifs / videos via the first e-mail in the readme file.
Have a great Sunday!