Swimmers itch also known as duck itch. It’s a reaction to the skin when you have come in contact with water from a lake or pond. Any water that maybe contaminated with these little water borne parasites. (Mostly in slow moving water). That attach themselves to you. With in hours you have this intense itching. It’s not serious just very bothersome and normally doesn’t last more then a week. Try swimming in a pool where these little parasites couldn’t strive.