Issued by the Republic of Niger in 1966, this 50 Franc stamp commemorates the Décennie Hydrologique Internationale (International Hydrological Decade) which spanned from 1965 to 1974. The design features symbolic scientific and industrial imagery, including water-related equipment, pipelines, and infrastructure — highlighting global efforts in water research and management. It was part of a broader UNESCO initiative to promote better understanding of the Earth’s water resources. Designed by Gauthier, the stamp blends shades of violet, blue, and red in a dynamic composition.