The bag, containing more than a thousand 10,000-yen notes, was hauled out of the sea off the coast of Ofunato city in Iwate Prefecture, reports the Mainichi Daily News.
Its total contents amounted to 11 million yen, or around 145,000 dollars.
The fishermen who found it promptly handed it in to the local authorities.
There was nothing else to indicate the owner's identity.
The authorities are not releasing full details of the catch, to make sure that only the rightful owner can identify the bag.
They believe the cash must have been swept away in the tsunami. City official Kou Ueno told the Press Association:
"We think it is related to the disaster as no-one is going to throw this kind of thing away on purpose."
Members of the public have been very diligent in reporting tsunami treasure to the authorities. Safes and envelopes filled with cash have been handed over since the disaster "in droves," Ueno said.
If no one claims the money within six months, it will go to the fishermen who found it.