Breaking in a horse... in water (hidden camera)

I observed these horses being broken in in the Dominican Republic. This may seem odd and unusual (horsewhisperer this aint), but its an interesting and quick way to get a horse used to a rider. The water was not particularly deep, but just deep enough to slow the horse's movements and make it possible for the rider to climb up. Is this cruel? Possibly. But the horses seemed only annoyed afterwards and surprisingly calm.