Popular boating sport on whitewater river waters is whitewater kayaking. The levels of the kayaking can be from simple active/moving water to more extreme and demanding conditions. Whitewater kayaking consists of five sub-categories: riverrunning, creeking, slalom, playboating and squirt boating. The first, riverrunning, is the most essential form of the sport. The other four types have evolved from this category to push the difficulty levels and challengers presented by riverruning. Creeking is done on difficult rapids that are usually graded 4-6 and require much technical skill. Typically, this category involves running ledges, slides and waterfall with higher gradients on tighter and smaller rivers. Some people consider these activities done on larger rivers. The technical and competitive category is known as slalom. It is also the only whitewater event that is included in the Olympic Games. The goal is to move from the top to the bottom in a pre-determined section of a river as quickly as possible. While doing so, participants must also navigate double-poled vertical gates over the river. The freestyle form of whitewater is known as playboating, which is both artistic and more gymnastic than other forms of  kayaking. Instead of moving down a river or body of water, playboaters remain in one location on a wave or something similar where they perform movements and tricks while working both with and against the current of the river. The final sub-category is squirt boating, which makes use of low-volume boats while doing a variety of special moves in the water. The boats used in this category are usually flat, quite long and light in design as it was a prelude to playboating.