Water in gas??

[buickspec6231]

So I got the boat ready for its first launch of the 2011 season last weekend. I put the muffs on it fed the outdrive some water and the boat started up great with just a splash of gas dumped into the carb. I ran the boat for about 25-30 minutes and it was flawless, with several slow throttle accelerations. Today I went to take the boat out and take my Mom for a cruise. I went to the gas pumps and figured I would treat the boat to a tank of 93 octane, there was about a quarter tank of a lower octane fuel left in the tank and the tank is now 3/4 full. Well, when I launched the boat it started right up and idled fine. The boat even pulled away from the dock fine. When I went to slowly accelerate the boat stuttered, and quit. The boat would restart at first but would chug along for a few seconds and eventually die out. During this chugging the engine had a heavy knock which sounded like it was more of piston slap than a rod. Oil pressure is pretty steady at 35lbs. Eventually the engine wouldn't fire at all. Long story short I was forced to swim in 40* water to drag the boat to some strangers dock and tie up for a while. Engine is a '86 chevy 4 cylinder 181ci 3.0l w/ Rochester 2GC carb. I did the usual check for spark/fuel... checked the points and checked dwell. all of that checked out. I guess the real question is can water in the gas cause the engine to knock like that?? We have had a record setting month of rain here in CNY this year, and I have a feeling the 93 octane isn't flying out of the stations with prices the way they are and is fouled by water.... I'm going to ditch the fuel that I bought and fill up from a different station and see if it helps... I was just looking for other opinions, and if I missed anything. The good thing is, my Mom hadn't made it to the docks yet, so I didn't have the embarrassment of having someone else on the boat with me.