In the winter we use to ride a lot on the beach, non of the horses or ponies ever had thrush or mud fever, (scratches)
Sea water is brilliant stuff for healing wounds too.
I had a pony that had been lame for over six months with a bad wire cut across his heel. When I returned home with the pony I led him down to the beach and he was in the water for about an hour, it cleaned the wound right out and sea treatment every other day healed it in weeks.
When a horse/pony came to us with laminitis, we would lead it to the beach, find a breakwater with a deep puddle at the end of it and tie the pony to it for a couple of hours, they always walked home better .