Another parameter used to assess and monitor environmental impacts on species and ecosystems is connectivity or habitat fragmentation. This is used in the Danube and has been used to try to predict the possible impacts of dam development in the Mekong River, where planned dams would drastically reduce ecosystem connectivity in the Lower Mekong Basin. A key issue in relation to ecosystem connectivity is the barrier effect to up- and downstream fish migration. The impacts of dam developments in the Columbia and Mississippi rivers on the fish stocks clearly document the damage of habitat fragmentation on migratory fish.