So some friends were arguing over a ruling on the brabazon yesterday. 6th hole water left (in sight) water right (out of sight). My friend hits the ball right and is not 100% sure if the ball is lost or in the lakeas they have never played there before there are also trees and bunkers blocking sight. He plays a provisional ball and hits that in the left lake.. Splash! As its stableford they walk up the hole and my friend says i will drop one out of the hazard and play 3 from there, assuming it did go in the lake despite them not being 100% sure. The argument was if he has played a provisional then that counts as a drop from the lake but he was playing a provisional on the basis that the ball was lost as he didnt know there was water right as it was hidden by trees and bunkers.
What would be the ruling on this what are you supposed to do if you think the ball is lost or wet?