Waitangi River at Watea

The Waitangi River originates in roughly the middle of Northland and flows East where it joins the coast at Waitangi. There are two sites on the Waitangi River that form part of the river network, one at Waimate North and the other at Watea near Waitangi. The catchments of both sites are dominated by pastoral farming. However, the geology of the upstream site at Waimate North is predominantly volcanic acidic, while the site at Watea is dominated by hard sediments. Unlike many of Northland's rivers, a riparian buffer strip of vegetation exists along the majority of the Waitangi River. The Watea site on the Waitangi River is one of four sites in Northland that are part of the National River Water Quality Network administered by NIWA.

The 2005-2006 results for the Waitangi River at Watea site are summarised in the table below including the median, range and percentage of sampling occasions that comply with relevant guidelines. Note: Nutrient results were only available for seven sampling occasions (July 2005 – January 2006), except for total phosphorus and nitrogen and the results for June 2006 where not available at the time of data analysis. Medians shown in red are outside the recommended guidelines.

Parameter Median Range % comply with guideline
Temperature (deg. cel.) 16.4 12 - 22.4
Dissolved oxygen (mg/L) 9.9 7.4 - 11.1 100
Dissolved oxygen (% Sat.) 100.5 84.5 - 104 64
Conductivity (mSm) 11.8 9.4 - 13.7
Water clarity (m) 1.62 0.14 - 2.78 82
Turbidity (NTU) 2.6 1.0 -34 82
E. coli (n/100mL) 118 53 - 6488 55
Dissolved reactive phosphorus (mg/L) 0.004 0.003 - 0.018 71
Total phosphorus (mg/L) 0.018 0.012 - 0.085 80
Ammoniacal nitrogen (mg/L) 0.008 0.002 - 0.034 71
Total nitrogen (mg/L) 0.42 0.204 - 1.05 80
pH 7.5 7.0 - 7.7 91


The 2005-2006 results show that the Watea site has similar water quality to the Waimate North site further up the Waitangi River. However all medians for the Watea site are within recommended guidelines and water quality tends to be good (i.e. parameters met the guidelines) for 50 to 80% of the sampling occasions.

Again bacterial contamination is the most concerning result. Although six of the 11 samples were below the recreational bathing guideline of 126 E. coli/100mL, there was still some extremely high results such as on 15 September 2005, where it peaked at 6488 per 100 mL. This spike in bacterial contamination was associated with increased flow and is likely to be a result of surface run off.

Based on data from October 1996 to May 2006, the trend analysis shows that there is a significant decreasing trend for nitrate (NO3) of 0.009 mg/L per year at a 95% confidence interval (not shown in the trends table) for the Watea site on Waitangi River, however there was no significant trend for total nitrogen. There was no significant trends for any of the other parameters.