In many ways, deltas are a river system’s “grand finale.” After meandering hundreds or thousands of miles, a river’s velocity decreases as it enters a larger water body, depositing nutrient-rich sediment and forming a vast network of waterways.
These diverse deltaic wetlands — found from the Arctic Ocean to the Mediterranean Sea to the Kalahari Desert in Botswana — are home to innumerable plant and animal species. Fertile delta soils form some of the most agriculturally productive landscapes in the world, including the Nile Delta in Egypt, the Sacramento–San Joaquin Delta in California and the Mekong Delta in Vietnam. Given their economic and ecological significance, half a billion people worldwide call river deltas home.
But deltas are disappearing. Human alterations to river systems are eroding deltas and starving them of sediment while sea-level rise threatens to turn deltas around the world over to the ocean. Saving these unique and diverse ecosystems is becoming a priority among researchers, engineers and government officials alike.