"Electrum" is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. So essentially what you're saying is: You have a lead to "barrels" (albeit small barrels) of this material. Not sure what percent is gold, and what percent is silver, But even assuming a 50/50 mix, you're talking millions of dollars worth (??) once you weigh it out. For example, even a SINGLE cigar box sized brick of gold, would take 2- men to lift, and would allow you to retire for life. MUCH LESS "3 barrels".
And your concern is the ability of the barrels to hold up under water ?
Here's what I'm seeing in this question: Someone comes on who's got a lead for a treasure worth millions. Often time they phrase it in past tense "found", because they've narrowed it down to a certain lake bottom or cave. But now it's merely a matter of minor details. Eg.: a detector that goes 6 meters deep. Or whether or not the barrels hold up under water. Mind you, they haven't "found" anything yet, or substantiated their lead. Nonetheless, they're already working on the other details of where to smelt it. How to overcome legal govt. obstacles, heavy equipment to bring to the surface, etc...
So have you considered that the lead, itself, might be only a ghost story camp fire legend ?