When trying to get a line across a wide stream, many attempt dragging the line behin a boat and ferrying straight across.  Seems like it makes sense, the shortest distance between two points is a straight line.  Unfortunately the current drives the boater and rope downstream in a pendulum arc.  We use pendulum arcs all the time when tossing throw ropes from shore to swimmers, works great in that application. 

Lets think about a variation on this method.  Instead of trying to go straight across, start the boat as far upstream as the rope will allow.  Perform the same ferry and the arc will land him on the other side roughly straight across the stream.  This is known as a reverse pendulum.  Just make certain you have more rope than needed to guarantee success - at least 1.5 times the width. 

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.

The rivers we paddle have a very wide variety of features and topography.  Some of the challenges you might face are dense brush, boulders in the way, very fast water, ledges, shallow and slippery slides, river bends, etc.  Take a few minutes to assess the situation.  Don't fall into the tunnel vision trap, look upstream and downstream as well.  In one of the SWR classes I took, students resorted to paddle wading to cross a fairly wide stretch of river.  I ran upstream and quickly swam across.  They were still wading 20 minutes after I had crossed.  My flat water swim was much safer as well.  In a recent class, we had to exercise the line crossing exercise in a narrower area.  I thought I was giving the students a challenge by drawing an imaginary line 30' back from the stream edge.  One bright student said he could toss the rope the roughly 90' distance.  Not convinced I said go for it.  He simply tied together a couple of 1/4" lines, fed out one of the bags, and then threw the first bag overhand in a bulls eye to the person on the other side.  This is an ingenious adaptation of the messenger line approach used by fire departments - simply brilliant.

When we start scenarios, we will often exercise a wide variety of skills.  Take a foot entrapment on a wide portion of the river in fast rapids for example.  It may be very difficult to paddle a kayak out to the victim and hold them, you need an alternate plan.  Perhaps a stabilization line will help.  The trick is crossing over 100' of raging rapids in a timely manner.  Every situation is different and sometimes you need to be creative.