The MV Nyerere ferry overturned near the shore between the islands of Ukora and Bugolora.
It is thought the overloaded vessel toppled over when crowds on board moved to one side as it docked.
Local media say the ferry’s official capacity was 100 people. Officials have confirmed that the vessel was carrying more than 400 passengers when it capsized.
About 100 people were rescued while 37 are said to be in a critical condition.
Mwanza Regional Commissioner John Mongella said that 42 more deaths had been confirmed on Friday, after 44 on Thursday.
Exact figures, though, are yet to be confirmed – Reuters said the person who dispensed tickets for the journey also died, with the machine recording the data lost.