If you’re going to throw a boulder or rock off a bridge, throw it parallel to the creek/river and not straight down.

Throwing a big rock straight down into the river will create a pillar on the riverbed. Throwing it parallel will result in the rock naturally sliding to the bottom and resting on the riverbed with minimal change to the depth. <br>This means safer waterways for kayakers and less chance of a lawsuit if someone gets hurt.<br><br>Edit: I’m a whitewater kayaker and have had too many close calls with rock pillars to count. Usually when we find them we’ll try to recruit someone to pull them down with a pulley rope system.