To improve water quality we need to stop the pollutants getting into our waterways. This is achieved by planting on the river banks so that surface water runs through vegetation and soil, both of which can filter it before it enters the receiving waterway system. Planting on the river bank can also increase the amount of shade over the waterway. Shade helps to keep water temperatures down which helps to minimise the growth of algae. Ensuring that there is plenty of water in the waterway also helps.
It is also important to allow floods to occur, since these help to flush out the waterway.