One of the fastest ways to cross portions of a stream is to swing the swimmer on the end of a throw line in a pendulum. The belay person acts as the base of the pendulum and the water current speeds the traversal. They can be hooked on a rescue vest tether, great for holding an impaired victim or simply holding on with their hands over the shoulder. An extra person on shore can speed the process by holding on to the line and simply walking down the rope using the vector pull technique. The belay person can also retreat further up the bank to increase the angle and speed landing on shore. This is great for breaking a strong eddy line. For longer traverses, you can set-up a chain of belay persons. After each individual pendulum sweep, bring the person back up your eddy and hand them the end of the next throw rope to continue their traverse across the stream. This is similar to how Tarzan traversed distances via swinging on vines in the jungle. This video shows a variation of a zip line crossing:Zip Line Crossing.
You can also try pulling the swimmer directly across via a tag line. It helps to have multiple pullers, especially when the current is stronger. Simply keep pulling up the slack via moving your hand positions down the line towards the swimmer. This technique works best in calmer water as a steadying measure for wading.
Another useful approach reminds me of a children's telephone line. This approach strings together several ropes. This can be quite useful when there are obstructions in the way. The first person tosses to someone midstream. That person tosses to another further across the river, and so on. Tie the ends together and take up the slack.