Quick answer: Unreal Water Body collision shape staying stale after spline edits? Collision regenerates only on save - call BuildWater or save the level.

Reshaped a river's spline. Visual updates instantly; AI agents still treat the old shape as water.

Call BuildWater

Editor > Water > Build Water. Regenerates collision meshes from current spline data.

Or save the level

Saving triggers rebuild as a side effect. Often the simplest workflow.

Listen for spline changes

For tools that edit splines programmatically, call RebuildCollision in the edit completion handler.

“Water collision is generated. Generation needs an explicit trigger.”

Add 'Build Water' to your pre-PIE checklist. Saves the AI-walks-through-river bug class.