My friends pony won't go in water?

One thing that you can try is a trick developed by Clinton Anderson who uses this mostly on horses who refuse to trailer, but the same concept applies here as it does there. You want your horse to go somewhere, and they wont go. What you do is you move that pony's feet forwards, backwards, left and right when next to the river. Make being outside of the water a chore. Then when he is a little bit tired, try to get him to go into the water. If he takes a step into the water, let him stop and rest and get his breath back. Resting is a reward to him now! I suggest starting it by the stream where he can already cross. Work him beside the river, then let him rest when his feet are in the water. Eventually you can try it by the lake. Hope it helps :)