Take a couple of pounds of pellets, carrots, etc and something to set them on so they are not in the dirt. Put him on a long rope, you cross the creek after you've let him smell the goodies. Place these on the ground and bend your head over and look at it. He will think you are eating something he's not getting. This is a big decision for him so try to be patient. When he crosses allow him some then cross back and repeat. Keep doing this until the feed is gone. Then head home, he's done well. When next you ride, take some carrot chunks and when he crosses the creek reward him with a piece. He will start to look forward to crossing water. One of the reasons crossing water is a problem is because of the horse's limited vision. Because of this he will either try to splash it away or drink it away. To him it could be an abyss he could fall in to. Your offering feed strengthens the bond and he is learning to trust.