As more and more people move into cities and towns, a number of factors cause environmental problems. More houses, buildings, factories and infrastructure like roads, sewage systems and electricity needs to be supplied. People need work and need industries are created. This increases waste and pollution production. More food is needed and therefore more natural area is converted to agricultural land. This invariably leads to an increase in fertiliser and pesticide use. Not only is more water used in this process but water pollution increases.
When it rains fertilisers drain into rivers and dams. Sewage spills into water bodies has the same effect. This results in an increase in nutrients (nitrates and phosphates) in the water and water plant growth increases known as algal blooms. When this plant material dies and decays the bacteria uses the oxygen in the water. The lowering of oxygen levels results in the death of other water life that needs oxygen to survive, like fish. This is called eutrophication and may cause disease and is unappealing to the eye. Water can turn a lime green.