This leaves no oxygen left for plants and animals. As well as this problem, pesticides reaching rivers and seas can kill animal life. Industrial discharge also contains metals such as mercury which can have effects on the nervous system and lead to kidney disease. The main problem with this type of pollution is the health risk to humans. Mainly causes by sewage and oil.
Bathers can get upset stomachs and eye infections.
In the short term there is a risk of typhoid and salmonella and polio in the long term. This includes nitrates from farms and metals. The long term effects of sewage sludge are not yet known. This spoils beaches and more importantly kills wildlife. Caused by oil leaks but more often tankers washing out at sea.