Waiarohia Stream at Whau Valley Road

Waiarohia Stream is a small stream originating from Pukenui Forest and the Western Hills in Whangarei. The upper catchment is mainly indigenous forest with some exotic forestry. The stream flows through a small area of low intensity farm land with mostly lifestyles blocks, before it reaches residential housing and the central business area of Whangarei. This site is located upstream of the majority of residential housing in the upper catchment of the Waiarohia Stream. It was added to the network in 2005-2006 as a background site to compare the urban Second Ave site to.

The first year of results for the Waiarohia Stream site at Whau Valley Road are summarised in the table below including the median, range and percentage of sampling occasions that comply with relevant guidelines for the 12 sampling occasions. Medians shown in red are outside the recommended guidelines.

Parameter Median Range % comply with guideline
Temperature (deg. cel.) 16.2 12.5 - 20.2
Dissolved oxygen (mg/L) 9.5 8.1 - 10.6 100
Dissolved oxygen (% Sat.) 97.5 88.7 - 102.7 33
Conductivity (mSm) 29.8 15 - 46.9
Water clarity (m) 0.88 0.34 - 1.52 92
Turbidity (NTU) 6.9 3.7 - 34 25
E. coli (n/100mL) 726 179 - 12033 0
Dissolved reactive phosphorus (mg/L) 0.007 0.002 - 0.018 75
Total phosphorus (mg/L) 0.067 0.041 - 0.155 0
Ammoniacal nitrogen (mg/L) 0.005 0.005 - 0.02 100
Total nitrogen (mg/L) 0.784 0.414 - 0.954 17
pH 7.2 6.8 - 7.5 67


This is the first year of results so limited conclusions can be drawn at this stage; however the 2005-2006 results highlight several areas of concern in the Waiarohia Stream. Similarly to the Second Ave site bacterial levels are consistently elevated, with none of the samples meeting the recreational bathing guideline of 126 E. coli/100 mL. Total phosphorus and total nitrogen are also often elevated, with their medians for 2005-06 exceeding their respective guidelines. Turbidity and water clarity also appears to be an issue at this site on several occasions.

The source of the nutrient and bacterial contamination is likely to be surrounding small scale pastoral farming and related to the direct access that stock have to the stream in many places.