AFor horses that are afraid of crossing water, the most effective approach I know is to pasture them with a stream. The stream will change over the course of a year and get them used to crossing various depths and currents. They may not immediately cross voluntarily when first pastured with a stream. If they are with other horses, they usually start crossing with the herd whenever it crosses. But if they are not with other horses or they stay behind the herd so that they don’t have to cross, you can start offering feed on alternate sides of the creek.

In some areas, it can be difficult to find a pasture with a natural stream, so then it is back to patient behavior modification using systematic desensitization and positive reinforcement for every increment of improvement. For most horses, this is best done with a companion animal to lead the way. For some step-by-step procedures and tips on this type of behavior modification, see "Overcoming Obstacles Your Horse Fears" for an answer to a similar question about railroad tracks.