Heavy rain can flush into ponds organic matter from fields, parks, and forests. Storms can also cause sewage to overflow. Especially after drought when the land hasn't had a wash for a while and soil is more prone to erosion.
Sudden rain can bring high amounts of nutrients rich in carbon, nitrogen, and phosphorus, into ponds, rivers, lakes and oceans. This phenomenon has been particularly pronounced after last summer of droughts and devastating bushfires, which burnt the vegetation cover in catchments of many water bodies. Burnt and decimated bush is less effective in stopping topsoil and ash to be flushed away.
Having more nutrients in water may sound like a good thing and it is surely good for algae that feed on them. However, too much of a good thing for algae is a bad thing for fish and a diverse range of other organisms that need to compete with algae for breathing space.
If too much algae live and die in a pond, the bacteria that feeds on their dying and decomposing bodies depletes oxygen that fish need. Oxygen is further reduced at night by algae's respiration, which can make fish suffocate. This is not a problem only for fish. We do not want toxic algae in drinking water supplies or recreational waters either.
Luckily, there are steps we can take to prevent this. If we protect our forests, if we plough, fertilise, and pesticide our farming land thoughtfully, and if we take better care of livestock, all this will improve the health of our water bodies. It will also be good for the health of our own bodies through living in a less polluted environment and having healthier produce to eat.
In urban areas, creating more buffer zones by replacing impenetrable concrete and asphalt surfaces with natural cover, makes our cities more liveable. It also allows storm water to soak into groundwater reservoirs instead of being flushed off into waterways, causing floods and pollution downstream. Upgrading old wastewater and sewage infrastructure should also be on the list of priority projects.
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