Driving through them slows down your vehicle, and if you are hit with the flame thrower while wheel-deep, you will take extra damage. The same is true of your enemies, however, so be sure to capitalize when they put themselves at a disadvantage. The ramps up to the refinery also take you up to a couple of pipelines, which are basically portals to other parts of the arena.
Pipelines often yield special weapons and power-ups, so are usually worth the effort.
There are some sweet power-ups in a small bay, but if you are doing fine on land, it's best to stay there. Some quests require you to take to the waves, so grab that hydro mod, and have at it. This arid wasteland is the most wide-open of the arenas. Meteors fall randomly throughout the arena. When they land, they ripple the ground and toss your car, inflicting minor damage.