Water mob doesn't move

To give some background, I tried creating a water mob for the mod that I'm working on at the moment. However, when running the client, the mob didn't try to swim or move around at all, instead staying stationary in the water. I know that people have had similar problems before but going through the few forum posts related to my issue, nothing worked. If anyone has a potential solution that would be great, and thanks in advance to anyone reaching out.