From Walking to Swimming
You can use these leading and lungeing exercises to gradually move your horse farther into the water, first up to his ankles, then knees and so forth, making small circles in and out of the water. Eventually, your horse will begin to swim part of the circle.
Once the horse is no longer just walking, it is absolutely critical to stay forward of his withers, but not in front of him. When he begins to swim, the horse will bring his hind legs way up under his belly, then stretch them to the side, then way out behind him. It's easy to get kicked by a hind leg stretching in a motion you don't expect.
Continue making larger circles, entering the water at one spot, moving down the shoreline and coming out at another spot. Occasionally, have him walk into the water, stand and relax, then back out.
Horses are extremely powerful swimmers once they get the idea. Normally, horses breathe very loudly when swimming, probably due to the amount of pressure of the water on their lungs. They should swim with their ears, eyes and nose above the water's surface.
Some horses will act as though they cannot swim, and in fact, they can't, at least not yet. They may drop their bodies to the floor of the lake and then push off with their hind legs, surging up like a submarine coming out of the water. Others get a little water in their ears and start shaking their heads while swimming - making them uncoordinated in their movements. Others may try to run over you, the way a panicky foal comes crashing into his mom.
Occasionally, a horse will really panic and start frantically paddling, sometimes with his head under water. You have to keep calm and encourage them back to shallow water by guiding their head with the lead rope.
When you've taken every precaution you know to take and you feel sure that it's OK to get into water deep enough that you and the horse can swim safely, you can begin swimming alongside him. Stay up by his head but out to the side, because both his front and hind feet will be swimming. Just like you did as a kid, horses have to learn to swim, so make sure that you don't encourage your horse into deep water until he has become an accomplished, confident swimmer.
You should do your own swimming. Don't expect to hang onto your horse in order to stay afloat. A remarkably small amount of pressure can push your horse's head under water. Watch that you do not pull him under with the lead rope, either.
Riding Into the Water
When you and your horse are old swimming pros, you might want to ride him into the water bareback. When he gets deep enough that he'll have to swim, slip off him and swim up by his head. Don't ride him as he swims. Stay ahead of his withers on the left side and hold the lead rope with one hand. You'll "steer" the horse by pushing his nose in the desired direction.
If the horse swims faster than you do, or he gets so far out ahead of you that you are about to lose control of him, let the lead rope go. Do the same if he panics or gets scared and starts bobbing around. He will likely be able to get himself out of the water, but you don't want to risk getting injured by a flailing hoof while he does so.
Be particularly careful if you and a friend are both swimming your horses. Stay a reasonable distance from them because a horse's hind legs can stretch quite a ways behind him.
Swimming is one of the most aerobic activities that animals can do. A 10-minute swim is equivalent to a several-mile canter, so don't overdo it. After just a few attempts, your horse will probably be breathing pretty hard, as will you. Go to shore and let him catch his breath. It is supposed to be fun for both of you. You can always come back another afternoon to let him get in shape for longer swims.
