River habitats and the dolphins which live in them are highly vulnerable to the effects of a wide variety of human activities. The river dolphins are under increasing threat principally from entanglement in fishing nets, pollution through pesticides, heavy metals and effluent from industries, and the construction of dams for irrigation and hydroelectric power.
The latter are of particular concern. Dams may reduce the dolphins' food supply, by preventing migratory fish from reaching their spawning grounds, and restrict the flow of fresh water, therby exhausting nutrients and oxygen supplies. More curcially, they restrict the dolphins' natural feeding range and separate dolphin populations into small, isolated groups that cannot interbreed and therefore do not have enough genetic variability to survive.
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