I wouldn't think some milky oil would have shut down the engine. Unless there is so much water that a cylinder(s) seized from "lack of oil". Then I would think you should notice a difference on the dipstick. So, aside from a head gasket, the only places water can see oil is the water pump (as I previously discussed) or the O-rings that are in the block where the cylinders go into it. I would start with the water pump as it's the "cheapest". Then it's a matter of starting at the top. Remove one head at a time until something is evident. If you find a blown head gasket, I'd do all three. If the gaskets are fine, then you're into cylinder removal. This is such a simple engine. That's about all the places water can mix with oil. I also wonder if when you "hosed" it if you put water in a "pocket" somewhere that got dislodged with boat action away from the dock.....but I'd think that's pretty far fetched but maybe another oil change could be worth a try now that you're back at the dock....But, I wouldn't think it would be enough to shut it down. If you have the metric tools and want to spend some time with disassembly, be glad to help. If you do that, I'd talk to the mechanic and make prior arrangements if you need help with reassembly. Save $100/hr........Was there any chance of freezing over the winter? (I think you're in the lake?)