Mill Stream is a spring-fed tributary of the Wairau River. The stream holds a unique position amongst Marlborough's surface waters in being the longest spring fed stream in the region. It is highly prized as a source of freshwater for
both domestic and agricultural use. Water quality of the stream has come under scrutiny with many complaints around
the perceived deterioration of the water quality and consequently problems with the ability of some landowners to use the water.
A monitoring programme was established to determine the state of water quality in the stream. Several sites along the length of the stream and its tributaries were sampled on a monthly basis for a year. The results establish a baseline which defines the current state of water quality.