Take a look at this picture. The long sides of each triangle are meeting points, junctions between fast and slow water, known as creases. A crease is the most important feature for anglers on a rainfed river. They are major feeding lanes, bringing trout a seemingly endless supply of insects – aquatic or terrestrial. Trout and grayling will take up position along these lanes. Fish are opportunistic, always on the lookout, so these areas will always be attractive, at any point in the day. Slower water, away from the crease, offers fish a resting opportunity. It can be a good area to target with dry-flies. Fish tend to be looking up for potential prey items that will be silhouetted against the sky due to the less broken surface. In fast, turbulent water, fish must have a good reason to expend energy, so only food items in good numbers make it worth their while spending long periods of time in this area. However, in dry, hot summer weather, in reduced flows, there may be comfort for fish in this more oxygenated water.