Which activity primarily involves the use of rivers for sport or leisure?

The activity that primarily involves the use of rivers for sport or leisure is gorge walking. This adventurous outdoor activity typically takes place in scenic locations where participants walk through river gorges, often involving climbing, jumping, and navigating through shallow waters and rocky landscapes. Gorge walking is specifically designed to provide thrill-seekers with an experience that integrates outdoor physical activity with the enjoyment of natural river environments.

In contrast, the other choices focus on activities not primarily connected to the recreational use of rivers. Agriculture may utilize rivers for irrigation or water supply but does not mainly involve sports or leisure. Urban planning refers to the strategic development and organization of towns and cities, which may consider river locations but is focused on infrastructure and land use, rather than recreational activities. Sewage disposal involves the management of waste and is directly concerned with sanitation rather than leisure or sports activities. This highlights how gorge walking is uniquely suited as a leisure activity centered around rivers.