A man using a metal detector has helped police unearth four submachine guns at Lake Hume.
The father had been using the device near Ebden Reserve on Sunday afternoon when he found a Thompson firearm.
Police searched the area, near the water's edge, and found a further three "Tommy" guns.
While the weapons are closely associated with prohibition era America in popular culture, Wodonga Detective Sergeant Graeme Simpfendorfer said they were used in the Australian military about the time of World War II.
"These type of firearms were made just after World War I and didn't come into service with the British, American and Australian forces until after World War II," he said.
"We're working with a large amount of time.
"They could have been here from any time from after World War II to now.
"These weapons are more commonly known for the time of prohibition in America.
"As to their use for us here, it's more military style.
"They're not able to be purchased."
In other news:
Officers and the military police returned to the area on Monday to search for more weapons.
The guns are inoperable and there is no risk to the public.
The wooden stocks have disintegrated or were removed before burial.
Lake Hume is about 21 per cent full, and the weapons would have been underwater for a lengthy period.
Police urge anyone with information to contact them, or call Triple-0 if a gun is found.
Investigators are working with historians on the find and don't believe the weapons are linked to any offences.
It's not the first time weapons have been found at Lake Hume.
A large quantity of ammunition, hand grenades, detonators, and anti-tank rounds were found near Bethanga Bridge in April 1945 after the water dropped to a low level.
Police believed the items were stolen from railway trucks or a military camp and dumped.