The journey by road from the Lake Victoria port of Bukoba to Mwanza is a rough one even by African standards: 12 hours on a creaky bus on a dangerous, rutted track. So most Tanzanians prefer going by ship, a cramped but usually reliable overnight trip on one of the government-owned ferries that operate along the southern shore. "On the ship," says Imelda Njunwa, a Mwanza housewife, "we never thought about death." Now she and most other lakesiders can think about little else.

In the deadliest disaster in the history of Lake Victoria navigation, the passenger ship MV Bukoba capsized last week in calm waters some 10 km northwest of Mwanza, drowning more than 500 on board. Among the dead were some 40 children returning from their final exams in a government school in Bukoba. Most of the victims remained trapped inside the steel hull as the ship went down, and by week's end hundreds had yet to be recovered from their watery tomb. As reports emerged that the ship was grossly overloaded and unstable, President Benjamin Mkapa called for a government investigation of the causes of the accident.

The disaster plunged Tanzania into mourning, and in Mwanza thousands stood vigil throughout the week on the rocky shoreline watching for boats that might be returning the bodies of their loved ones. Njunwa's eldest daughter Lillian was among the lost. Lillian was returning from a visit to her grandparents. "We don't even know where to put the cross," said the mother last week from her darkened home, where she, friends and relatives had gathered to weep for the lost girl.

The lake waters were smooth as the ship set out from Bukoba at 10 p.m. on Monday, May 20, bound for its next port of call, Kemondo Bay, just 20 km away. But when it docked there, hundreds of travelers who had been denied passage at Bukoba, and had journeyed to Kemondo by truck, rushed the gangway and flooded onto the boat, settling in every available open space. "There was no place to move. We could not even lie down," a passenger recalled.

As the ship left the bay and turned south, it listed ominously and stayed heeled over for several minutes before righting itself. Throughout the night passengers felt a strange rocking motion, even though the waters were comparatively still. Then, as the ship steered south again toward Mwanza port early on Tuesday morning, it heeled violently to the right. The crew ordered all passengers to move to the other side of the vessel. But as they shifted, the ship listed badly to the left and capsized. "I took off my jacket, I took off my shoes and I jumped in the lake to save myself," says Ramadhani Rashidi, 59, a businessman traveling in first class. "We started to swim without knowing where we were going."

He was fortunate. Most of those in second- and third-class cabins were unable to jump clear. The ship rolled onto its side, then turned turtle, trapping hundreds of passengers underneath. Cleophace Kamala was among them. When the boat turned over, he and another man managed to swim to an air pocket where they and a young girl clung to piping to breathe the remaining air. "There were so many bodies of women and babies and old people in the water," recalls Kamala, 43. "We were there for many hours. We banged on the [hull] with pieces of wood." Finally the girl, exhausted, let go. In a desperate effort to escape, Kamala dived down past the submerged corpses and found an open porthole.

Another survivor, Justin Rwakatare, gripped a loading crane and managed to swing free as the ship keeled over. But when six women clung to his life jacket and dragged him down, he was forced to shift to a bunch of bananas, helping two young children onto his makeshift raft. Later they found a life belt and floated for three hours. With a rescue ship in sight, the younger child, a girl of about eight, "started crying," recalls Rwakatare, still distraught at the memory. "She said she was too tired, and then she said goodbye. I tried to hold on to her, but she was sinking and pulling me down. I let go. The ship was so close. But she could not hold on."

The first rescue ship took at least an hour to arrive. Saleh Songoro, who owns a small shipping company in Mwanza, traveled out in one of his own vessels. When he reached the upturned hull of the Bukoba, it was rocking imperceptibly and settling deeper into the waves as air bubbles escaped. "We could hear people knocking on the hull," Songoro says. But there was no way to reach them. Finally, a crew from the Tanzania Railways Corp., which operates the ferries, arrived with oxyacetylene torches and began cutting into the side of the ship. The first hole allowed two passengers to squirm free, but when the workers burned a second opening, it proved disastrous. The remaining air escaped and the vessel disappeared. It was 3 p.m. on Tuesday. "We were all very quiet," says Songoro, whose wife had four sisters and 16 other relatives on the ship. "There were so many people still inside."

With no passenger list available, the exact number of victims is still unknown. The government estimates that 661 passengers were on board when the ship left Kemondo Bay. With just 114 survivors, the death toll would be 547. But another unconfirmed report from the International Federation of the Red Cross suggests that as many as 800 may have lost their lives. What is certain is that many hundreds of travelers were anxious to board the ship last Monday night. Ordinarily a much larger ferry, the MV Victoria, makes the Bukoba-Mwanza run. But the Victoria was called in for repairs earlier this month, leaving hundreds of passengers who had bought tickets on the larger vessel without a means of travel.

An official with the Tanzania Railways Corp. last week called the accident a "mystery." Transport Minister William Kusila acknowledges that the ship was overcrowded, but he claims the registered cargo of 8.5 tons was well below capacity and should have allowed for the additional weight of passengers. The best source of information on the tragedy, the ship's captain, is either unwilling or unable to talk. At the hospital in Mwanza he sits in bed in neat, blue-striped pajamas and motions to his head, indicating amnesia and shock. "He is not in his right mind," claims Kusila.

While overloading clearly contributed to the calamity, those familiar with lake travel point out that the ships have been carrying excess weight for decades. "Overcrowding is normal here," says Erik Pitersen, a Danish technician who has been working on the ships under a program funded by his government. "It cannot be just one reason that led to this accident." Another Western engineer who asked not to be named was more specific. "It is obvious to all people with a technical background that there was a problem with the ballast," he told a reporter. Earlier this month the Bukoba underwent stability tests by Belgian engineers. During these, ballast tanks along the ship's keel, which ordinarily carry up to 100 tons of water, were emptied. If they had not been properly refilled by Tanzanian workers, or if the system of pipes and valves used to replenish the tanks malfunctioned, that, combined with the overcrowding, would explain the ship's instability, the technician said.

Such explanations, of course, offer little comfort to the bereaved families. For Njunwa, the loss of her daughter Lillian's body is particularly painful. Throughout the week she and her relatives continued to make periodic trips to the port and to the hospital morgue to scan the bloated faces of those recovered from the lake. But with hope fading, she and other mourners plan to conduct an ancient ritual in which relatives of lost drowning victims weave a white shroud, weight it with rocks and lower it into the lake to placate watery spirits who might claim others in the same way. "It is all we can do," says Njunwa. Future travelers on Lake Victoria can only pray that the ritual works.