You can throw a log into water and then step on it. When you first occupy it two things happen:
1. rolls a check based on how heavy you are and dexterity and luck where you may fall off onto an adjacent tile (fairly low chance).
2. Dunks the log under the water and causes you to take a round of normal water tile exposure (so not ideal for piranhas unless you have a ton of hp), then the momentum carries it forward for a number of turns decided by your weight. If you're very light (perhaps corruption or just inventory dependent) it won't dunk but it also might fail to move enough and leave you stranded.

Obviously when logs bonk into other obstacles, including other logs, the appropriate stuff happens.