Human activity can have a negative effect on the water environment:
- Sewage disposal in developing countries is expected to cause 135 million deaths by 2020. In the UK we add 1,400 million litres of sewage to our rivers daily although most of it has been treated
- Chemical fertilisers contaminate groundwater as well as river and water supplies. These add nutrients to the water leading to an increase in the growth of algae downstream. Occurred along the shores of the Gulf of Mexico.
- Industrial waste – every year the world generates 400 billion tonnes of industrial waste which is pumped untreated into rivers, seas etc. Heavy metals such as lead, and mercury become concentrated in rivers.
- Dams – trap sediment in reservoirs which reduces floodplain fertility and the flow of nutrient from rivers into seas.
- Abstraction – removing water from rivers and groundwater sources can cause issues: in arid areas rainfall can never recharge underground stores and the removal of freshwater from aquifers in coastal locations can lead to salt water incursion.