Next to our school, there is a sump. This is a space, with a monoculture of bulrushes, that collects storm water as part of the suburban drainage system.  The storm water drains from the sump into the Swan River. Storm water contains pollutants, including chemicals like pesticides and herbicides and nutrients from fertilisers like nitrogen and phosphorous.  These pollutants are detrimental to the health of the river and the animals that rely upon it.