There are hundreds of category 1 and 2 water pollution incidents every year in England.
According to the Environment Agency, there were 317 serious pollution incidents to water in 2016. It says that agriculture is now the largest sector responsible for significant pollution events to water.
The agency says that the overall number of water pollution incidents has reduced in recent years, with the number of serious category 1 incidents falling by almost two-thirds between 2001 and 2016.
The animated map shows the locations of category 1 and 2 water pollution incidents over time.