North Kawhia
Catchment monitoring by the Kawhia Harbour Care commenced in May 2022.
It covers eight sites sampled on a quarterly basis. There are five monitoring sites in North Kawhia and four sites in South Kawhia. Waikato Regional Council (WRC) has one monitoring site in the lower Oparau River (North Kawhia), which is monitored monthly.
A water quality baseline was calculated from the time the catchment group was formed using five years of monitoring data (Jan 2016 – Dec 2020). The data was collected monthly at the WRC site.
The location of the four monitoring sites in South Kawhia are shown on the right.
South Kawhia– Key Resources Being Lost from the Land
Monitoring results show the key resource being lost from the South Kawhia catchment is E. coli. E. coli represents a loss of organic matter and nutrients, as it is largely associated with animal manure in rural catchments.
The water quality dials summarise the results collected from the 4 sites in the South Kawhia catchment. The dial on the left shows the baseline for the catchment, covering 5 years of regional council monitoring at Oparau River, representing 58 samples. Note the national bottom line for water clarity/suspended sediment has been adjusted on the baseline dial to match the river environment classification for south Kawhia (Hard Sedimentary). The dial on the right combines all data collected at the four sites in 2025, representing 16 samples. Arrows indicate either an increase or decrease in values compared to the sub-catchment baseline levels. An increase in water clarity is positive for river health while an increase in all other indicators may impair river health.
In 2025, nutrient and water clarity/suspended sediment indicators met national water quality limits while E. coli did not. Compared to the (Oparau River) baseline – Water clarity was slightly better, nutrient levels were higher and there was no difference in the overall rating for E. coli.
Full Report Available to Download
Water quality dials for the South Kawhia catchment.
The bottom dial shows the sub-catchment baseline (2016-2020)
The top dial combines results collected in the 2025 monitoring period.
2025 Quarterly Summaries
February 2025
Water quality was Excellent in Mangatangi stream (Site 38), Good in Ngahuinga stream (Site 35) and Oteke stream (Site 37) and Fair in Puaroa stream (Site 36).
E. coli concentrations were low in Oteke stream (120 cells per 100 mL) and Mangatangi stream (190 cells per 100 mL), slightly elevated in Ngahuinga stream (370 cells per 100 mL) and elevated in Puaroa stream (650 cells per 100 mL), exceeded the recommended health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were very low across all sites (≤ 0.10 mg/L), falling well below ecological toxicity threshold (2.4 mg/L). Mangatangi stream had the lowest concentrations (0.003 mg/L) and Ngahuinga stream had the highest (0.10 mg/L).
Ammonia concentrations were very low across all sites (≤ 0.008 mg/L).
Dissolved inorganic nitrogen (DIN) concentrations were also low across all sites (≤ 0.10 mg/L), falling well below ecological impact threshold 0.5 mg/L.Phosphorus:
Dissolved reactive phosphorus concentrations were low in three sites (≤ 0.007 mg/L) and were slightly elevated in Oteke stream (0.011 mg/L).Suspended sediment/Water Clarity:
Water clarity was excellent across all sites, relative to the national bottom line (0.61 m). Mangatangi stream had the highest water clarity (3.94 m) and Puaroa stream had the lowest (1.48 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Sample collection day: 3rd March 2024
2025 Quarterly Summaries
February 2025
Water quality was Excellent in Mangatangi stream (Site 38), Good in Ngahuinga stream (Site 35) and Oteke stream (Site 37) and Fair in Puaroa stream (Site 36).
E. coli concentrations were low in Oteke stream (120 cells per 100 mL) and Mangatangi stream (190 cells per 100 mL), slightly elevated in Ngahuinga stream (370 cells per 100 mL) and elevated in Puaroa stream (650 cells per 100 mL), exceeded the recommended health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were very low across all sites (≤ 0.10 mg/L), falling well below ecological toxicity threshold (2.4 mg/L). Mangatangi stream had the lowest concentrations (0.003 mg/L) and Ngahuinga stream had the highest (0.10 mg/L).
Ammonia concentrations were very low across all sites (≤ 0.008 mg/L).
Dissolved inorganic nitrogen (DIN) concentrations were also low across all sites (≤ 0.10 mg/L), falling well below ecological impact threshold 0.5 mg/L.Phosphorus:
Dissolved reactive phosphorus concentrations were low in three sites (≤ 0.007 mg/L) and were slightly elevated in Oteke stream (0.011 mg/L).Suspended sediment/Water Clarity:
Water clarity was excellent across all sites, relative to the national bottom line (0.61 m). Mangatangi stream had the highest water clarity (3.94 m) and Puaroa stream had the lowest (1.48 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Sample collection day: 3rd March 2024
2025 Quarterly Summaries
May 2025
Water quality was Good in Oteke stream (Site 37), Fair in Ngahuinga stream (Site 35) and Puaroa stream (Site 36) and Poor in Mangatangi stream (Site 38).
E. coli was very low in Oteke stream (47 cells per 100 mL), slightly elevated in Ngahuinga stream and Puaroa stream and elevated in Mangatangi stream (630 cells per 100 mL), exceeded the recommended health guidelines for swimming (540 cells per 100 mL). All other sites fell within health guidelines for swimming (540 cells per 100 mL) and Oteke stream met guidelines for livestock drinking water (< 100 cells per 100 mL).
Nitrogen:
Nitrate concentrations were low across three sites (≤ 0.38 mg/L) and moderate in Mangatangi stream (0.59 mg/L). All sites fell well below ecological toxicity threshold (2.4 mg/L).
Ammonia concentrations were low across all sites (≤ 0.01 mg/L).
Dissolved inorganic nitrogen (DIN) concentrations were low in three sites (≤ 0.39 mg/L) and slightly elevated in Mangatangi stream (0.60 mg/L), exceeding ecological impact threshold 0.5 mg/L.Phosphorus:
Dissolved reactive phosphorus concentrations were slightly elevated in three sites (0.012 - 0.016 mg/L) and very high in Mangatangi stream (0.082 mg/L).Suspended sediment/Water Clarity: Water clarity was Excellent across all sites (≥ 1 m), relative to the national bottom line (0.61 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Collection date: 15th May 2024
2025 Quarterly Summaries
August 2025
Water quality was Excellent in Ngahuinga stream (Site 35), Puaroa stream (Site 36) and Oteke stream (Site 37), and Fair in Mangatangi stream (Site 38).
E. coli was very low in Oteke stream (51 cells per 100 mL) and low in the other three streams (≤ 250 cells per 100 mL). All sites fell well within health guidelines for swimming (540 cells per 100 mL) and Oteke stream met guidelines for livestock drinking water (< 100 cells per 100 mL).
Nitrogen:
Nitrate concentrations were low across three sites (≤ 0.49 mg/L) and moderate in Mangatangi stream (0.81 mg/L). All sites fell well below the ecological toxicity threshold (2.4 mg/L).
Ammonia concentrations were very low across all sites (≤ 0.005 mg/L).
Dissolved inorganic nitrogen (DIN) concentrations were low in three sites (≤ 0.49 mg/L) and slightly elevated in Mangatangi stream (0.81 mg/L), exceeding the ecological impact threshold 0.5 mg/L.Phosphorus:
Dissolved reactive phosphorus was low in three sites (≤ 0.008 mg/L) and slightly elevated in Mangatangi stream (0.014 mg/L).Suspended sediment/Water Clarity was Excellent in Puaroa stream and Oteke stream (≥ 1.17 m) and Good in Ngahuinga stream and Mangatangi stream (0.77 & 0.86 m), relative to the national bottom line (0.61 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Sample Collection Day: 7th August 2024
2025 Quarterly Summaries
November 2025
Water quality was Excellent in Oteke stream (Site 37) and Mangatangi stream (Site 38) and Fair in Ngahuinga stream (Site 35) and Puaroa stream (Site 36).
E. coli was low in Oteke stream and Mangatangi stream (≤ 250 cells per 100 mL), falling within health guidelines for swimming (540 cells per 100 mL). However, concentrations were very high in Ngahuinga stream and Puaroa stream (1,300-1,500 cells per 100 mL). No sites met guidelines for livestock drinking water (< 100 cells per 100 mL).
Nitrogen:
Nitrate concentrations were low across all sites (≤ 0.24 mg/L). All sites fell well below the ecological toxicity threshold (2.4 mg/L). Ammonia concentrations were very low across all sites (≤ 0.017 mg/L).
Dissolved inorganic nitrogen (DIN) concentrations were also low at all sites (≤ 0.24 mg/L), falling well below the ecological impact threshold (0.5 mg/L).Phosphorus: Dissolved reactive phosphorus was very low in all sites (< 0.004 mg/L).
Suspended sediment/Water Clarity was Excellent in three sites (1.72-3.13 m) and Good in Puaroa stream (0.88 m), relative to the national bottom line (0.61 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Sample Collection Day: 15th December 2025.
North Kawhia
Data & Downloads
Aquatic Biodiversity Summary
Biodiversity monitoring includes eDNA, collected by KCRC, and traditional biodiversity monitoring techniques (netting of freshwater invertebrates and netting and electrofishing of freshwater fish), by Waikato Regional Council (WRC). eDNA sampling has been done by KCRC, in autumn and winter in 2021, 2022 and 2023. WRC monitors most sites every 1 to 2 years, between November and March. If more than one results is available for any single monitoring location the results for that site are averaged across years.
Both North and South Kāwhia have significant freshwater biodiversity value, however, some sites are showing early signs of ecological stress.
Just under halve of freshwater invertebrate MCI scores are good.
The number of insect species detected from eDNA (an indicator for ecological health) were low in Te Kauri stream (North Kāwhia), 17 species and moderate in Puaroa stream (South Kāwhia), 39 species.
Fish communities were diverse across north and south Kāwhia.
Three whitebait species were detected, Giant kōkopu, Banded kōkopu and inanga.
Six species of threatened fish present, including lamprey, Īnanga, Giant kōkopu, Longfin eel, Redfin bully and Torrentfish.
Only 1 species of introduced fish was detected, brown trout.
