If you do not want to risk having your Pikmin drown or be burnt to death, you can punch these Blowhogs to death as just Olimar, Louie, or the President of Hocotate Freight. Stand facing the Blowhog's eye, at about a 45 degree angle to its snout, and repeatedly press A to punch it. Stand back a bit, and not directly against it, and you will not be hit by its stream of fire or water, or its lunging attack.