In addition, the BBC and other news agencies have reported that two individuals are being held in connection with the accident following orders issued by a Russian court. The director of the company that leased the tourist boat and a ship registrar who certified it have been detained.
The double-decker vessel sank while executing a turn near the Kuybyshev Reservoir, a wide expanse of the Upper Volga.
The death toll is expected to rise, with at least 85 of the victims having been identified, according to the Emergency Situations Ministry. Seventy-nine passengers and crew were saved when they were scooped out of the water by another river boat or used makeshift rafts to make it to shore.
The ship was transporting at least 208 people (the number has continuously fluctuated), far more than the 120 it was licensed to carry.
While an investigation has been launched as to cause of the sinking -- Russia's worst maritime disaster in three decades -- the Moscow Times reports that portholes left ajar because of a lack of air-conditioning may have contributed to the tragedy when a wave crashed against the ship's side and flooded the vessel.
The newspaper says weather may also have been a factor, as squalls were reported shortly before the Bulgaria sank in more than 60 feet of water. Because the ship went down in a matter of minutes, only a few of the lifeboats were deployed, and survivors report that at least two passing ships ignored them floundering in the water.
Spokesman Vladimir Markin of Russia's Federal Investigative Committee confirmed investigators were also looking into reports that the boat was listing to the right when it left port. Additional allegations have arisen that the boat lacked a license to carry passengers and that it had a malfunctioning left engine, which passengers had complained about on previous trips.
The vessel, built in the former Czechoslovakia, is said to have had dozens of cabins and two restaurants. This is the peak season for tourism on the Volga, which is lined by many of Russia's largest cities.
According to the New York Times, "River cruises are a beloved summer pastime for Russians, who sometimes book rides through the country's vast inland waterways that last for weeks. ... The boats often stop at uninhabited islands in the river so passengers can disembark and swim."
--by John Deiner, Managing Editor