Water pollution is best understood as a chain: source, pathway, affected water, consequence and prevention.
Four source pathways
Industrial discharge can carry chemicals if it is not properly treated. Sewage can contaminate water when collection or treatment fails. Agricultural run-off can carry fertilisers, sediment or pesticides from land after rain. Plastic waste can break into smaller fragments and travel through rivers and seas.
Effects
Pollution can damage aquatic habitats, reduce water quality and create risks for people and wildlife. The exact effect depends on the pollutant, amount, exposure and water system, so not every incident has the same outcome.
Prevention ladder
Prevent pollution at the source, collect and treat waste water, reduce unnecessary chemical loss from land, keep litter out of drains and protect wetlands and riverbanks. Clean-up after contamination is usually harder than prevention.
Original river file
After heavy rain, muddy water and fertiliser-rich run-off entered Reed River from an uncovered field edge. The response added a vegetated buffer strip and changed storage practice. Investigators then monitored nutrient levels upstream and downstream; the file does not state a final result.
Water-pollution reading
After heavy rain, fertiliser left near a fictional field edge moves in run-off to Reed River. A buffer strip is added and nutrient levels are monitored upstream and downstream before and after several rain events. The plan tests one pathway; it does not show that every pollutant has the same source or effect. Students analyse supplied records only and do not collect water or handle chemicals.