Because so many salts (not just NaCl) can contribute to salinity, it is measured indirectly as the ability of the water to conduct an electric current (uS/cm). It is considered that salinity levels should not exceed 1500 uS/cm for the lower reaches (Maribyrnong at Keilor) and 500 uS/cm further upstream (Sunbury and beyond). We often record levels above these, reflecting the geology of the area rather than a pollution problem.
Measurements have been separated into sites upstream or downstream from Sunbury. It is interesting to note the trend to increasing salinity after the confluence of Riddells Creek with Jacksons Creek and further as the stream flows towards the Maribyrnong - see bar graph. (To advance, click link below.)