I'm building a Frogger clone and am creating all the assets myself.

While I have some art experience (mainly traditional art), this is the first time I'm trying to create pixel art for a video game. Below is an initial mock-up with some sample sprites and background tiles.

I've been experimenting with the best way to make the logs/turtles not appear hovering on the water, hence the light outlines around some of them. Is there a better way to achieve that effect?

I'm sure there is a lot than can be improved, so any and all advice is appreciated!