The flood waters that inundated a large swath of Pakistan and forced millions of people out of their homes are starting to recede in some areas — but humanitarian organizations are warning that the need will linger long after the water has poured into the sea.

More than 1,600 people have been killed and an estimated 17.2 million people have been affected since the heavy floods began in late July, the United Nations says.

The UN has called for $460 million US to meet immediate relief needs — a financial goal it has yet to meet — and reconstruction costs are expected to run into the billions, the International Monetary Fund says.

Pakistani villagers return to their areas as floodwaters begin to recede in Karampur, in southern Pakistan, on Wednesday. (Anjum Naveed/Associated Press)

"We've had a lot of issues with getting Canadians to pay attention to this crisis and donate," said Nicolas Moyer, co-ordinator of the Humanitarian Coalition, a network of four Canadian humanitarian organizations that work to raise awareness and funds during crises.

He said donations increased after the federal government announced the creation of the Pakistan Floods Relief Fund, a program that will see the federal government match donations made by individual Canadians to eligible charities. But the initial spike has largely tapered off, he says.

The program was announced on Sunday, Aug. 22 and applies to donations made between Aug. 2 and Sept. 12. The funds raised will be an addition to the $33 million the Canadian government has already pledged.

Moyer says the Humanitarian Coalition — made up of Care Canada, Oxfam Canada, Oxfam Quebec and Save the Children Canada — has raised roughly $1.4 million for Pakistan since the floods started. Roughly $600,000 of the funding came in during the first week after the government announced the matching program, he said.

About half of that increase came in between Monday to Wednesday right after the announcement, he said.

"The boost of the matching fund program has largely dissipated," he said.

Caroline Riseboro, the vice-president of public affairs at World Vision Canada, said her organization saw a 33 per cent increase in donations right after the matching program was announced.

"But after that, it has been slow," Riseboro said, noting that it has been a challenge to raise awareness about the slow-moving crisis, particularly as coverage of the floods moves off the front page of newspapers.

Zaid Al-Rawmi, a spokesman for Islamic Relief Canada, said his organization also saw a spike after the program was announced, but he noted that donations have "tapered off a little" as time passed and media coverage decreased.

Aid must be scaled up: UN

The floods that have swamped the Indus and its tributaries are gradually declining, officials say, but Pakistani government leaders and top UN officials say aid efforts still need to be scaled up.

Flood victims and their children wait to be treated in an overcrowded private clinic offering free support for victims in Sukkur, in Pakistan's Sindh province on Wednesday. (Damir Sagolj/Reuters)

For people like Ziarat Gul, an Afghan refugee who spent three decades building a new life in neighbouring Pakistan, the needs are pressing. He told The Associated Press that the floods wiped out the life he built for himself and his family.

"I am left with only the clothes I am wearing," the 60-year-old said from the Azakhel refugee camp, roughly 150 kilometres from the capital, Islamabad.

Pakistan's economy is also at risk, as the floods have destroyed millions of hectares of crops and could lead to soaring inflation and job losses, Pakistan's Prime Minister Yousuf Raza Gilani said Wednesday.

"The crisis is far from over," said Tammy Hasselfeldt, chair of the Pakistan Humanitarian Forum, a consortium of non-governmental organizations.

"In fact, we are now entering the most difficult stages. Unless we can act fast enough, children and other vulnerable people may succumb."

UNICEF's executive director Anthony Lake said Monday that more needs to be done to stave off a potential "second wave of disease and misery for millions of families."

More than 1.2 million homes have been damaged and millions of people are still in need of shelter, and clean water and food are still in short supply in some areas, the UN says.

Skin diseases, respiratory infections have hit many flood victims and more than half a million people have been treated for diarrhoeal diseases, the World Health Organization says.

Médecins Sans Frontières, or Doctors Without Borders, is distributing tents and clean water, and running mobile clinics to help treat flood victims across Pakistan.

Rebecca Davies, the fundraising director of Médecins Sans Frontières Canada, said MSF Canada is raising money for Pakistan but is not participating in the government's matching program in order to maintain independence and security for its workers in the field.

"There are real security implications for the way we do our fundraising," Davies said, adding that MSF relies entirely on private donations to fund its medical relief programs in Pakistan.

She said some potential donors choose to give to other charities that are participating in the matching program — but she said roughly 75 per cent of donors who contact MSF Canada still choose to donate to the organization's flood relief program.

The most important priority, the aid groups say, is continuing to provide support to relief and reconstruction programs after the sense of urgency fades.

"The impulse to give wanes, but the need doesn't. The need is only growing," Davies said.

With files from the CBC's Jennifer Walter and The Associated Press