Fertiliser on farmland
Rainwater running off farmland into rivers and then out to sea also causes problems in the sea. When soil is washed away along our tropical coasts in Queensland, and Western Australia, coral reefs are damaged. Coral polyps must have clear clean water to survive. Coral needs the sea to have very low nutrients. When fertilisers used on farms are washed into the sea, algae can take over from coral.
When trees are not properly removed from forests they can also cause soil and silt to be washed into the sea.
Pigs are mostly farmed in buildings. The concrete floors must be regularly washed down to remove the pig poo. The smelly water and poo must be treated on the pig farm before it is released to be soaked up by the soil.
Usually factories and mines follow regulations that are designed to prevent polluting chemicals from being washed into the sea. But sometimes accidents occur and rivers and the sea get polluted.