When a Racer moves onto a space containing Terrain, first resolve any Ram that may have occurred (and any effects resulting from the Ram), then resolve the Terrain's rules, as listed below:

Water - Gain a Stagger token. Any movement remaining on your current Movement Die (if any) is reduced to 0. If you Staggered onto the Water Terrain and still have Staggers to resolve, do so.

Rocks - If it is your Movement Turn, your Movement Turn immediately ends (even if you are currently Staggering).

When a Barrel enters a space with either type of Terrain, first resolve any Ram that may have occurred, then the Barrel is discarded.