Farming communities on the Mauritanian and Senegalese sides of the Senegal river valley are under threat because of drought, the US-based famine early warning agency Fews Net has said.
Floods have been followed by drought
In Mauritania farmers have been reduced to collecting wild plants and almost all are eating only once a day, the agency said.
And the prices of imported wheat and rice have risen sharply.
In Senegal, peanut and millet production has dropped, leaving farmers increasingly reliant on money sent to them by family members living in towns, Fews Net's local representatives have said.
The World Food Programme (WFP) is about to re-assess the situation in the area.
"The Senegalese have a coping mechanism. But on the other side of the river, the situation is completely different," the WFP's Senegal representative Richard Verbeeck said.
"They have no relatives to send them money or the ability to sell small amounts of produce."
The Mauritanians of the Senegal river valley had their livestock wiped out in freak floods in 2001. This is the third drought they have faced in as many years.
Some farmers on the Senegalese side of the river have been able to find employment in tourism by moving to the coast and have received some government help.
But in Mauritania, social assistance and job opportunities are virtually non-existent.
Both Senegal and Mauritania are recognised as countries which face problems feeding their populations.
In Mauritania, desertification is progressively diminishing the amount of arable and pastoral land.
And an estimated 36% of children under five suffer from malnutrition, according to the WFP.
In Senegal, population growth, land degradation and the declining prices of main exported commodities on the world market have caused a severe and prolonged economic recession.