More than 100 people are feared dead after a ferry capsized in Tanzania.

The MV Nyerere was traveling between the islands Ukerewe and Ukara on Thursday when it overturned, according to The New York Times.

Investigators believe overcrowding led to the tragedy given Thursday is market day, and packed boats routinely ferry shoppers to the area. The boat was designed to carry 100 passengers and 25 tons of cargo. It is suspected that over 300 people were onboard when it sank. So far, 136 bodies and 40 survivors have been recovered from Lake Victoria, reports the BBC.

It will be difficult to discover exact number of passengers onboard during the tragedy as the person responsible for ticketing drowned and a ticketing machine has not been recovered.

In a televised address, Tanzanian president John Magufuli instituted a four-day mourning period and ordered the arrests of those responsible for manning the vessel, according to The Citizen.

“The captain is already in police custody,” President Magufuli said. “I have also ordered that all those responsible for the operations of the MV Nyerere vessel be arrested for questioning.”

The president also said the vessel was carrying too much cargo, exacerbating the overcrowding.

“It is obvious that more bodies are trapped in the capsized vessels,” Magufuli said. “In fact, reports I receive show that even the cargo was far more than the 25 tons allowed. There were tons of maize, crates of beer, building materials. Passengers had also big pieces of luggage as they were going to an open market.”

Magufuli encouraged any witnesses to come forward to help with the investigation.

“We should let authorities do their job and if you have any evidence, you should wait until the matter is taken to court so that they could help the court deliver justice,” the president added.

The East African nation has a history of ferry accidents. The MV Bukoba sank in 1996, and it’s estimated between several hundred to 1,000 people perished. In 2011, 200 people died when the MV Spice Islander I sank off the coast of Zanzibar. A year later, 145 people died when the MV Skagit sank in the Indian Ocean.

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