5) dissolve oxygen

5. Scale of measures needed to address the pollution: Action within a single community is usually enough to stop point source pollution. It is because point source pollution has an identifiable source it can be said to be easier to tackle than nonpoint source pollution. Nonpoint source pollution tends to diffuse very widely. For this reason, nonpoint source pollution is often tackled through global action – for instance, by asking factories throughout the world to reduce their CO2 emissions and by asking private individuals throughout the globe to stop using their cars so often and to take global action. For nonpoint source pollution, smaller scale measures are usually needed. These might include fixing the chimney on a particular factory so that it emits less soot and smoke and plugging up leaks in pipes carrying sewage or chemicals
https://www.importantindia.com/24048/point-source-and-nonpoint-source-pollution/