More than 30,000 families have been pushed out of their homes in flooding that began in August.
The capital and many other places across the country have been inundated in recent weeks.
The fellows attended a one-week seminar in Washington in August before settling into US states based on their areas of interest.
Despite concerns, Lao officials are still pressing for construction.
United Nations officials say the capitals of Thailand and Cambodia are at risk as the worst flooding in modern times.
George Boden, a campaigner for the British watchdog Global Witness, recently spoke to VOA Khmer about the implications of such a policy.
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.