today my friends disc was about the width of a mini dry , the rest was all in the water, he claimed that since you could put a mini totally behind the disc he was alright, my other friend said that if you touch it down and more then half is wet then its o.b , my friend would not take the stroke.
As stated above if any of the disc is not in the OB water then it is in bounds and you get up to 1 meter releif perpendicular to the hazard. Sometimes when the disc is near the edge it is difficult to tell if it is OB or not, I like to take a finger or a stick and push it in on the side where the disc looks good, if it goes into water it is OB, land then it is safe. Some folks are too lenient in my opinion a disc near a bank is touching a leaf which is touching the bank some will say safe or safe benefit of doubt goes to the player but if you push down on the leaf and it is water underneath then it is OB. In your case should not really be an issue that disc is in!