Contaminated water that enters a river or stream from a concentrated source such as a pipe is referred to as a point source (top). Water that discharges from overland flow or subsurface seepage into streams is known as a non-point source (bottom). Contaminants from non-point discharges are more difficult to manage because they contribute small amounts from many locations, sometimes including faecal contaminants from grazing animals.
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Photographs by Graeme McKenzie
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