People who live in coastal regions may suffer the cumulative burden of environmental stress from the activities on and overcrowding of the coast and from upstream and inland development. If not properly managed, development can result in pollution, deforestation, and inadequate management of soil, water, pesticides, and fertilizers. Damming rivers can also have negative environmental effects, such as soil erosion and destruction of ecosystems that support various fish and marine mammals. When concentrated in small, confined, and overcrowded areas such as coastal zones, pollution and other problems pose greater threats to human health.