The news spells the end of the rescue operation, since the bodies of all 122 boat passengers, who were declared missing and presumed dead, have been found.
The cruise boat, which was partly raised last week and taken to shallow waters, is believed to have had problems with one of the engines. Besides it was overcrowded and operated without a proper license.
Investigators have arrested the tour operator and a local licensing official as they launched a criminal probe.
The Bulgaria sank in the middle of the river in the Volga region near the village of Syukeyevo in the Kansko-Ustinovsky district of the Republic of Tatarstan in the afternoon on July 10.
There were 173 people onboard when the boat went down.
The cruiser ship, which belongs to a local tourism company, was traveling from the town of Bolgar to the regional capital, Kazan.
The double-deck ship was built in Czechoslovakia in 1955 and its maximum capacity was 140 passengers.
The cruise ship had two restaurants, a bar, a music lounge, a beach deck and 1, 2, 3 and 4-seat cabins and one luxurious cabin.