In general, when running in a straight line the current is strongest in the middle and weaker near the banks.
 

The friction from the banks slows the current down and causes it to spiral. The surface flow can push a swimmer away from the bank therefore never assume that a swimmer is safe until they are on the bank. However it is get ashore against a helical current than when the main current sets into the bank.

In some man made structures with smooth sides the main current may flow right up to the sides.

It is essential for clear communication that all members of the group understand river right, river left and upstream,

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The main current always goes to the outside of the bend. The flow is fast and the water deep where it sets right into the bank. The current erodes the bank and can create undercut banks, exposed tree roots, fallen trees and debris that can act as a strainer.
 

On the inside of the bend the water is slow and shallow. There are small rocks/shingle banks where floods have moved them and then dropped them as the flood power decreases.

A strainer is any obstruction that leaves gaps that are large enough for the current to flow through but not big enough to allow a boat or swimmer through. A major role of white water leadership is to avoid strainers and that means avoidance strategies by anticipating their presence.