Authorities say at least 176 people have now died in flooding that began in August and has continued across the country.
Oxfam America said in a statement that government and relief agency responses are under way, but more assistance is necessary.
Many Cambodians believe they will be cursed by their ancestors if they are unable to pray at a pagoda during Pchum Ben.
Officials are still gauging the damage to infrastructure and rice fields, in the worst flooding since 2000.
The flooding has affected 90,000 families across 14 provinces, killing at least 34 children and destroying some 200 homes.
Cambodian health officials are carefully watching for the new Vietnamese strain to appear in the country.
Cambodia has about five known blocs for petroleum exploration in the Gulf of Thailand, as well as potential resources in Tonle Sap.
George Boden, a campaigner for Global Witness, expresses concerns to VOA Khmer about the future petroleum production in Cambodia.
According to the plan, the government will pay almost $500 per metric ton for white rice and $650 for higher quality fragrant rice.
In Cambodia, officials have curtailed dredging and suspended sales as they assess the environmental damage caused by sand mining.
The report urged more action at the grassroots, rather than national, level, to lessen the impact of climate change.
Villagers say their livelihoods there are being threatened by continuous government concessions to private rubber and other companies.