Wading is fast water is often a challenge.  Unfortunately, many river booties made these days have very slippery soles on wet surfaces.  Sometimes using a paddle as a cane isn't convenient.  If you have a rescue vest with a tether and someone to belay you from upstream, that line will provide a great deal of support.  It also provides significant safety since your belay person can quickly keep you from getting swept downstream should you slip and fall.  Using two lines as in a traditional v-lower is even safer.

Fast and deep water, waves, etc. can make it quite a challenge to maintain a consistent air pocket for a person on a v-lower.  It can also be a real challenge for a raft lower as it has a much larger surface area to catch the water.  Adding ballast on the downstream side of the raft can help to raise the upstream side high enough to avoid taking on water.  If you no longer feel your position is safe, use your quick release system.

Strong currents create a great deal of extra load on a V-Lower.  It may be difficult to stay on the surface and avoid turning over.  The V-Lower is just another technique.  Think about your situation and choose the safest and most reliable way to access the victim.

Sometimes you may be lucky and have a peninsula, boulder, or bridge that allows you to directly lower a rescuer to the victim using just one line.  This is much faster to set-up and can be a handy rescue method.  The rescuer still needs to avoid foot entrapment and use a proper safety vest.  Single ropes are also used in vertical rescue lowers, perhaps off a bridge.

You can support your head with your hands to keep it up and out of the water.  This also leaves the hands in an easy to see area for the shore teams so they will quickly notice when you are about to give a signal.  Don't forget to keep your elbows tucked in close to your body so they will not bang into anything.