If you swim into a 1 block night area you will crawl (land swim). When you go into 3rd person, you will mostly see black, like in the photo I provided. You will also have the walking particles bellow you

How to reproduce

1. make a long 1x1 tunnel
2. put on one end a hole in the top
3. put water in the hole
4. swim into it

when the water ends, you will keep swimming.