At least 251 Congolese refugees drowned in the weekend sinking of a crowded boat on Lake Albert, the Congolese government confirmed Thursday, declaring three days of national mourning.

The boat was travelling from Uganda, which sits across the lake from the Democratic Republic of Congo, and was transporting around 300 people who were returning home from refugee camps.

"It is with deep sorrow that we confirm to the nation the death of 251 of our compatriots who had boarded the boat from the Ugandan side of Lake Albert," government spokesman Lambert Mende told reporters.

Congolese President Joseph Kabila proclaimed three days of public mourning starting on Thursday "to show solidarity and compassion with the entire Congolese nation", Mende said.

The boat was transporting refugees who had fled fighting between the Congolese military and ADF rebels, and were returning home on their own initiative.

"These men and women, along with their children," had decided to leave the camp at Kyangwali because of the "poor quality of the welcome to which they were subjected," said Mende.

"They have unfortunately not followed the traditional method of repatriation, a method that involves the host country, in this case Uganda, the country of origin, the Democratic Republic of Congo, and the UN High Commission for Refugees," he said.

UNHCR said it was one of two boats leaving Hoima district on the eastern shore of the lake on Saturday.

READ: Double tragedy as boat carrying DRC refugees capsizes

The body count has mounted rapidly in recent days. Initial reports on Saturday said 20 had died, but this increased to 98 by Monday and 107 on Tuesday, including 57 children.

Navigation on central Africa's Great Lakes can be as perilous as sailing in high seas when the weather is rough. Accidents often lead to very high casualty tolls, partly because of a lack of life-jackets and also because relatively few people know how to swim.

Saturday's disaster happened just days after Congolese authorities launched a campaign to enforce the wearing of life jackets aboard all boats on the nation's many waterways.

Uganda remains a haven for refugees, according to UNHCR. While most of the new arrivals have fled conflict in South Sudan, the country is still home to 175,000 Congolese among a total of almost 329,000 refugees registered at the end of February.

The agency has in the past three months registered "a rise in the number of Congolese refugees spontaneously returning to the DRC", after the Congolese army last November won a major military victory over rebels of the Movement of March 23 (M23) in the troubled east.

Congolese people who decide to go home either cross Lake Albert or travel by road, the UNHCR added, saying a campaign to warn refugees of the risks of taking to the water was already in hand.