I was going to mention balance is also a key aspect of wading safely. Being able to recover when your foot slips to a new position and keep your balance could save you from getting flushed down river. Tai Chi or Yoga can help with core strength and balance tremendously. Ice skating is pretty good too.
Physical strength alone is not enough in my opinion. Both provide some other benefits, Hot Yoga like Baron Baptiste's is amazing for energy development and increase range of motion in addition to improved balance. The heat along with stretching can help improve range of motion from old injuries in a significant way.