Sure looks like it to me.
Great find, now let me clue you in on something that could possibly be great.
I found a similar watch once, it was near the bank of a lake and had to be there for years.
It came up black like yours, real thick and couldn't even wash it off in the water.
I brought it home and took a green scrubby to it and a whole lot of elbow grease and it took awhile but eventually I cleaned off a little patch of metal on the back and I almost fell over when I saw it.
You know how people keep talking about how gold and silver comes up out of the ground clean and you can usually tell them from junk and clad?
This is true most of the time but not all the time...and especially if any of that precious metal of either kind has been sitting in a moist environment for a long time.
I took my time and finally cleaned up my watch and it took hours of hard scrubbing but the results were, well, you can see it in the pics below.
Cross your fingers and scrub that thing, could be even better than you think.
Congrats and good luck!