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Phosphate levels should be less than 0.045mg/l for coastal plains (eg Maribyrnong at Keilor) or less than 0.025mg/l for uplands of the Maribyrnong (Sunbury and upstream). Excess phosphate (0.1mg/l or more) is of concern because it supports algal growth.

Measurements have been separated into sites upstream or downstream from Sunbury.  In 2012 (scan down below), phosphate levels were strikingly higher as the creek passed through Sunbury (see bar graph), possibly due to problems with old sewage pipes or to storm water runoff from the streets.  Note that the Sunbury Sewage Treatment Plant occurs between the Macedon St Bridge and Holden, but the problem begins upstream of the plant.  The phosphate is apparently diluted out by the time the stream reaches Organ Pipes National Park, except for one worryingly high result there.  However, results for 2013 and 2014, do not conform to this simple picture. 

In April 2014  there was one high observation at Emu Bottom, possibly due to overuse of superphosphate in that farming area.                                                                                                               
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Results for 2014:

Results for 2013:

Results for 2012: