I would think more modern too just because pocket knives tend to "decay" rather quickly being carbon steel. they usually had brass parts that last though
I’m going to agree with the masses, I think if it were a period pocket knife and spent that much time submerged under water it would be what we call in New England “wicked toastededer” than the one you have. Someone probably dropped that while fishing or camping. Still a cool find, I love to find old pocket knives!!!!!!
Old barlow or case 20s -45ish . The only thing that survives on them is the little brass plate . Sometimes there will be engraved initials on them . Keep digging those wonky offish signals .That little piece of brass is what made you dig unless you are digging everything .