Where do the primary threat to rivers come from?

The main threats to river basins (the entire area drained by a river) continue to mount.

Construction of large dams and physical alterations of river flow by straightening and deepening of river courses.

This disrupts the natural flooding cycles, reduces flows, drains wetlands, cuts rivers off from their floodplains, and inundates riparian habitats, resulting in the destruction of species, the intensification of floods and a threat to livelihoods in the long term.

thinking it would be physical characteristics