how could this possibly happen

[thedog]

My motors have had an issue this year coming out of winter storage, ran the boat fished hard last year up until december, then winterized and put it away.

last week I had issues with the motors running(first time I started it up this year)
after a week of trying I brought the boat to the dealer. he added some chemical to the fuel in tub after he pumped a bunch thru the filters and noticed a lot of water. then took the top sending unit off the tank and sticked it, 12" yes 12" of water in the fuel tank. I have always treated the tank with startron at every fill up. and in december had no issues.
the cap and vent were covered all winter with a full cover., over the entire boat, and i filled the tank up when I put the boat away.

either the fuel dock filled me with 40 gallons of water at the last fill, or someone stole my gas. but why would they fill the tank after taking out half of it.

could there be another issue? fuel tank has no oder under the deck breather is normal.
I am at a loss as to how 12" of water could get in the tank over the winter.