Streambed curvatures form different types of fish holding places. The outside bends or greater curvatures receive the current’s scouring actions. High flows cause a deepening of the riverbed channel. During low water conditions, holes and deep runs are present along with undercut stream banks. These quickly become favored fish holding places.
The inside or lesser curvature induces deposition of items carried by the currents. Here away from the main flow, food items settle. In addition, drifting insects are concentrated here.
Current seams are found as junctures between swift and slow flows. These seams can become favored lies that continually hold fish. Seams occur at both the great and the lesser stream curvatures. Seams are created by the shearing between fast currents and slower currents.
Islands generate additional current seams. Fish prefer the island’s seams because of a bonus of terrestrial insects coming from the island’s vegetation. An island’s placement provides a sort of wing foil with different current speeds on each side. The current seams occur on upstream sides, alongside, and downstream. The island’s vegetation enhances its bank-side cover. Stream braiding further enhances both the number of current seams and the bank-side
cover. The placement of an upstream riffle generates an open refrigerator door with insect emergence settling down back to the island. My favorite streams have lots of islands and channels because these structures enhance the number of fish producing lies.
A single island produces at least four different current seams. Two of them are further enhanced by bank side cover and undercut banks.
Even small islands with limited cover enhance the stream’s habitat. Here, mini-current shears, channels, and undercutting provide pocket water lies.
Don’t overlook small side channels in a large river system. But remember a prerequisite for productive habitat is a prior history of stable flows. It takes some time for fish to relocate if the minor channel has been recently dewatered.