(CNN) -- Heavy rains that began early in January in northern central Namibia have reached staggering proportions, with 80 people drowned and half a million others affected directly or indirectly, officials said.
President Hifikepunye Pohamba declared a national emergency in all six northern regions on March 28.
The affected region is in the Cuvelai Basin, which drains southern Angola via a complex of streams that typically result in an annual flood called the efundja, which is named for the fish that spawn in spring.
This year's efundja has resulted in the wettest year since systematic measurements started in 1891, with rainfall in affected areas nearly double the normal average.
Government figures cite 263 school closures, with a total of 320 affected, leaving 114,000 schoolchildren shut out of their classrooms.
Up to 40 health clinics are under water, and more than 100 health mobile outreach points have been made inaccessible as a result of damage to roads and bridges, according to the World Health Organization.
In addition, roads, bridges, homes and staple crops in all six northern and northeastern regions in Namibia have been destroyed, according to UNICEF.
They represent some of the country's poorest areas.
The Red Cross Society of Namibia estimates that 500,000 people have been affected, with the densely populated central-northern regions -- Omusati, Oshona and Ohangwena -- hit worst.
But other areas are also threatened, as rivers -- including the Zambezi -- drain southern and central Angola. Forecasters predict areas like Caprivi, which is about 500 kilometers (310 miles) east, may experience more flooding by next week.
About 40,000 people have been displaced, some 10,000 of whom have been accommodated in 68 camps set up by the government, officials said.
The death toll is expected to rise as water-borne diseases, mainly malaria, are predicted to spread.
The Red Cross and the U.N.'s Office for the Coordination of Humanitarian Affairs are appealing for help, and the U.S. government and some European countries have made donations. OCHA said in its southern Africa flood and cyclone report, published Wednesday, that 2011 marks the third consecutive year of heavy rains in the region. The result is that the water table has risen and that "flood water levels are unlikely to recede for the next three to six months."
More rain is expected.
Journalist John Grobler contributed to this report.