Thank you! Ha, sometimes they can be a little slow and squirmy. It is something I'm working on and I've got some substantial improvements since the demo by tweaking how the water applies drag. Getting them faster will also help the gameplay, since that way they can do more interesting things
P.S. One thing I thought I might mention is that if you seed in a lot of creatures at the start, you often tend to get stronger swimmers over time. It kinda gives evolution more to work with. If you are already seeding ~15 then you're good, but one person on the Steam forum was just spawning in a creature or two and then getting disappointing results.