Mangaotaki - Mairoa
Catchment monitoring by King Country River Care, commenced in 2021.
Across the entire Mokau River catchment the monitoring programme covers up to 16 monitoring sites across 6 sub-catchments sampled on a quarterly basis. Waikato Regional Council (WRC) has 5 monitoring sites in 4 of these 6 sub-catchments, which are monitored monthly.
A water quality baseline was calculated from the time the catchment group was formed using five years (Jan 2015 – Dec 2019) of monthly monitoring data, collected at the WRC sites.
The location of the monitoring sites for each sub-catchment are shown on Maps 1 through to 6, below.
Key Resources Being Lost from the Land
Monitoring across four sites in 2025 shows that the key resources lost from the Mangaotaki – Mairoa sub-catchment were E. coli and Sediment (reflected by low water clarity).
Loss of Sediment represents a loss of soil and nutrients.
Elevated E. coli represents a loss of organic matter and nutrients as it is largely associated with animal manure in rural catchments.
Catchment Hotspots
E. coli: Elevated at all sites - none met national health guidelines for swimming. Concentrations were highest at Mangaotaki River – SH3 Bridge and 11-Mangaotaki stream, and were lowest at Waitanguru stream.
Sediment: Suspended sediment was elevated at two sites - Kihikihi Stream and Mangaotaki stream, failing to reach the national bottom line for water clarity. Levels were also slightly elevated at 11-Mangaotaki River-SH3. The lowest levels were recorded in Waitanguru Stream which had a high median water clarity of 2.35 m.
The water quality dials summarise the results collected from the sites in the Mangaotaki – Mairoa sub-catchment alongside the Mokau River water quality Baseline. The dial on the left shows the baseline for Mokau River, covering 5 years of regional council monitoring at the five WRC monitoring sites (Awakau Road, Mokauiti Stream at 3-way Point Aria, Mangaotaki River-SH3 bridge, Totoro Road and Mangaokewa Road off SH30). The dial on the right combines all data collected at four sites in the Mangaotaki – Mairoa sub-catchment in 2025, 23 samples in total. Arrows indicate either an increase or decrease in values compared to the sub-catchment baseline. An increase in water clarity is positive for river health while an increase in all other indicators may impair river health.
In 2025, nutrient indicators and water clarity/suspended sediment met national water quality limits, while E. coli did not. Compared to the baseline – Water clarity and E. coli were higher. There was a slight reduction in dissolved reactive phosphorus and no difference in nitrogen compared to baseline levels.
2025 Quarterly Summaries
February 2025
Water quality was Fair across in Waitanguru stream (Site 10) and Kihikihi stream (Site 30) and Poor in Mangaotaki river (Site 11).
E. coli concentrations were very high across all sites (range = 1,300 to 1,400 cells per 100 mL), exceeding recommended health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were low to moderate across sites (range = 0.45 to 0.56 mg/L), falling well below ecological toxicity levels (2.4 mg/L). Kihikihi stream had the lowest concentration and Mangaotaki river had the highest concentration.
Ammonia concentrations were low across all sites (≤ 0.02 mg/L).
Dissolved inorganic nitrogen (DIN) was low in Waitanguru stream and Kihikihi stream (≤ 0.5 mg/L), falling just below the ecological impact threshold (0.5 mg/L). Mangaotaki river had slightly elevated DIN (0.58 mg/L).Phosphorus:
Dissolved reactive phosphorus (DRP) concentrations were low in Mangaotaki stream and Kihikihi stream (≤ 0.009 mg/L). Waitanguru stream had slightly elevated DRP (0.011 mg/L).Suspended sediment/Water Clarity: Water clarity was excellent in Waitanguru stream (3.35 m), good in Kihikihi stream (1.73 m) and poor in Mangaotaki river (1.21 m), relative to the national bottom line (1.34 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Collection date: 18th February 2025
Mokau River – Summary of water quality collected from 15 sites across the Mokau River catchment on 18th February 2025
Most sites had low nutrient levels, but elevated E. coli and poor water clarity were common, with a few locations exceeding human health and ecological health thresholds.
E. coli: 60% of sites had elevated concentrations (between 890 and 3,100 cells per 100 mL), 20% (3 sites) had slightly elevated concentrations (between 300 and 500), and 20% had low concentrations (≤ 170).
Nitrogen:
Nitrate: 100% of sites had low concentrations (range = 0.001 to 0.56 mg/L). Ammonia: 100% of sites were low to moderate (range = <0.005 to 0.200 mg/L). Dissolved Inorganic Nitrogen (DIN): 93% of sites had low concentrations (≤ 0.50 mg/L), and 7% (1 site) was slightly elevated (0.58 mg/L), exceeding the ecological impact threshold of 0.5 mg/L.Phosphorus:
Dissolved Reactive Phosphorus (DRP): 80% of sites had low concentrations (between <0.002 and 0.009 mg/L), 13% (2 sites) were slightly elevated (0.011 – 0.012 mg/L), and 7% (1 site) returned a very high concentration (0.024 mg/L).Suspended Sediment / Water Clarity: 47% of sites had good water clarity (A or B band), 7% (1 site) had fair water clarity (C band), and the remaining 47% had poor water clarity (D band). Bands for each site relate to the National Bottom Line (NBL) for water clarity and depend on landscape characteristics including geology, climate, and elevation. The NBL for Mokau River monitoring sites is either 1.34 m or 0.61 m, depending on local landscape characteristics.
2025 Quarterly Summaries
February 2025
Water quality was Fair across in Waitanguru stream (Site 10) and Kihikihi stream (Site 30) and Poor in Mangaotaki river (Site 11).
E. coli concentrations were very high across all sites (range = 1,300 to 1,400 cells per 100 mL), exceeding recommended health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were low to moderate across sites (range = 0.45 to 0.56 mg/L), falling well below ecological toxicity levels (2.4 mg/L). Kihikihi stream had the lowest concentration and Mangaotaki river had the highest concentration.
Ammonia concentrations were low across all sites (≤ 0.02 mg/L).
Dissolved inorganic nitrogen (DIN) was low in Waitanguru stream and Kihikihi stream (≤ 0.5 mg/L), falling just below the ecological impact threshold (0.5 mg/L). Mangaotaki river had slightly elevated DIN (0.58 mg/L).Phosphorus:
Dissolved reactive phosphorus (DRP) concentrations were low in Mangaotaki stream and Kihikihi stream (≤ 0.009 mg/L). Waitanguru stream had slightly elevated DRP (0.011 mg/L).Suspended sediment/Water Clarity: Water clarity was excellent in Waitanguru stream (3.35 m), good in Kihikihi stream (1.73 m) and poor in Mangaotaki river (1.21 m), relative to the national bottom line (1.34 m).
The results in the table below have been graded according to the National Policy Statement for Freshwater Management (NPS-FM, 2020).
Collection date: 18th February 2025
Mokau River – Summary of water quality collected from 15 sites across the Mokau River catchment on 18th February 2025
Most sites had low nutrient levels, but elevated E. coli and poor water clarity were common, with a few locations exceeding human health and ecological health thresholds.
E. coli: 60% of sites had elevated concentrations (between 890 and 3,100 cells per 100 mL), 20% (3 sites) had slightly elevated concentrations (between 300 and 500), and 20% had low concentrations (≤ 170).
Nitrogen:
Nitrate: 100% of sites had low concentrations (range = 0.001 to 0.56 mg/L). Ammonia: 100% of sites were low to moderate (range = <0.005 to 0.200 mg/L). Dissolved Inorganic Nitrogen (DIN): 93% of sites had low concentrations (≤ 0.50 mg/L), and 7% (1 site) was slightly elevated (0.58 mg/L), exceeding the ecological impact threshold of 0.5 mg/L.Phosphorus:
Dissolved Reactive Phosphorus (DRP): 80% of sites had low concentrations (between <0.002 and 0.009 mg/L), 13% (2 sites) were slightly elevated (0.011 – 0.012 mg/L), and 7% (1 site) returned a very high concentration (0.024 mg/L).Suspended Sediment / Water Clarity: 47% of sites had good water clarity (A or B band), 7% (1 site) had fair water clarity (C band), and the remaining 47% had poor water clarity (D band). Bands for each site relate to the National Bottom Line (NBL) for water clarity and depend on landscape characteristics including geology, climate, and elevation. The NBL for Mokau River monitoring sites is either 1.34 m or 0.61 m, depending on local landscape characteristics.
2025 Quarterly Summaries
May 2025
Water quality was Fair in Waitanguru stream (Site 10) and Mangaotaki river (Site 11) and Poor in Kihikihi stream (Site 30).
E. coli concentrations were low in Waitanguru stream and slightly elevated in Mangaotaki river and Kihikihi stream. All sites fell within health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were moderate across sites (0.63 - 0.80 mg/L), falling well below ecological toxicity levels (2.4 mg/L). Mangaotaki river had the lowest concentration and Waitanguru stream had the highest concentration.
Ammonia concentrations were very low across all sites (< 0.005 mg/L).
Dissolved inorganic nitrogen (DIN) was slightly elevated across all sites, above the ecological impact threshold (0.5 mg/L).Phosphorus:
Dissolved reactive phosphorus (DRP) concentrations were slightly elevated at all sites (0.011 - 0.014 mg/L).Suspended sediment/Water Clarity: Water clarity was Good in Waitanguru stream (1.56 m), Fair in Mangaotaki river (1.48 m) and Poor in Kihikihi stream (1.28 m), relative to the national bottom line (1.34 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
Mokau River – Summary of water quality collected from 15 sites across the Mokau River catchment on 15th May 2025
Water quality was Fair across the Mokau River Catchment. While most sites had low to moderate levels of E. coli, nitrogen, and phosphorus, and water clarity was good at over half the locations, a few sites exceeded ecological thresholds for nutrients and water clarity.
E. coli (Microbial Contamination):
Most sites (60%) had low concentrations (≤ 230 cells per 100 mL) low risk for swimming.
Two sites (13%) had very low concentrations (< 100), considered safe for livestock drinking water[1].
A third of sites (33%) had slightly elevated concentrations (370 - 490 cells per 100 mL).
One site (Puputaha stream) had high levels (690 cells per 100 mL) which could pose a health risk, especially when swimming.Nitrogen
Nitrate:
All 15 sites had low to moderate concentrations (0.06 - 0.80 mg/L), falling well below ecological toxicity thresholds (2.4 mg/L) for native fish and invertebrates.
However, 4 sites exceeded ecological impact thresholds (0.5 mg/L), which can affect stream health.
Ammonia:
All sites had very low concentrations (<0.005 - 0.08 mg/L), little concern for aquatic life.
Dissolved Inorganic Nitrogen (DIN):
Most sites (73%) had low concentrations (≤ 0.46 mg/L).
Four sites (27%) were slightly elevated (0.63 - 0.80 mg/L), exceeding the ecological impact threshold of (0.5 mg/L).Phosphorus
Dissolved Reactive Phosphorus (DRP):
Two-thirds of sites (67%) had low levels (<0.002 - 0.009 mg/L).
Five sites (33%) were slightly elevated (0.011 – 0.014 mg/L) which can contribute to problematic plant and algae growth if levels stay high.Suspended Sediment / Water Clarity:
Over half of sites (53%) had Good water clarity (A or B band).
Two sites (13%) had Fair water clarity (C band).
A third of sites (33%) had Poor water clarity (D band).
Water clarity bands for each site are based on the National Bottom Line (NBL), which varies depending on local landscape characteristics (e.g. geology, climate, and elevation). For Mokau River sites, the NBL is either 1.34 m or 0.61 m, depending on location.
[1] Drinking water for livestock should contain < 100 cfu/100 mL (median value) of E. coli. Livestock Drinking Water Guidelines (2023), Australian & New Zealand Guidelines for Fresh & Marine Water Quality.
2025 Quarterly Summaries
August 2025
Water quality was Fair in Waitanguru stream (Site 10) and Mangaotaki river (Site 11), and Poor in Kihikihi stream (Site 30).
E. coli concentrations were slightly elevated in all sites, though all sites fell within health guidelines for swimming (540 cells per 100 mL).
Nitrogen:
Nitrate concentrations were slightly elevated across sites (0.79 – 1.01 mg/L) but fell well below ecological toxicity levels (2.4 mg/L). Ammonia concentrations were very low across all sites (< 0.005 mg/L).
Dissolved inorganic nitrogen (DIN) was slightly elevated across in Waitanguru stream and Mangaotaki river (0.79 – 1 mg/L) and elevated in Kihikihi stream (1.01 mg/L), exceeding the ecological impact threshold (0.5 mg/L).Phosphorus: Dissolved reactive phosphorus (DRP) concentrations were low in Mangaotaki river and Kihikihi stream (0.009 mg/L) and slightly elevated in Waitanguru stream (0.012 mg/L).
Suspended sediment/Water Clarity: Water clarity was Fair in Waitanguru stream (1.48 m) and Poor in Mangaotaki river (1.26 m) and Kihikihi stream (0.96 m), relative to the national bottom line (1.34 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: 25th August 2025
Mokau River – Summary of water quality collected from 15 sites across the Mokau River catchment on 25th August 2025
Water quality was Fair across the Mokau River Catchment. While most sites had low to moderate levels of E. coli and phosphorus, 80% of all sites had poor water clarity and exceeded the ecological threshold for dissolved inorganic nitrogen.
E. coli (Microbial Contamination):
Most sites (73%) had low concentrations (≤ 240 cells per 100 mL), a low risk for swimming.
Three sites (20%) had very low concentrations (< 100), considered safe for livestock drinking water[1].
Four sites (27%) had slightly elevated concentrations (280 - 460 cells per 100 mL).Nitrogen
Nitrate:
Three sites (20%) had low concentrations (≤ 0.5 mg/L).
Twelve sites (80%) exceeded ecological impact thresholds (0.5 mg/L), which can affect stream health.
All sites fell well below ecological toxicity thresholds (2.4 mg/L) for native fish and invertebrates.Ammonia:
Most sites had low concentrations (<0.005 - 0.03 mg/L), of little concern for aquatic life.
One site (Huioteko stream) had slightly elevated concentrations (0.15 mg/L), which can impact sensitive aquatic species.Dissolved Inorganic Nitrogen (DIN):
Three sites (20%) had low concentrations (≤ 0.50 mg/L).
10 sites (67%) were slightly elevated (0.51 – 1.0 mg/L), exceeding the ecological impact threshold of (0.5 mg/L).
Two sites (13%) had concentrations exceeding 1 mg/L, which is of particular concern for aquatic life.Phosphorus
Dissolved Reactive Phosphorus (DRP):
Most sites (93%) had low levels (<0.002 - 0.009 mg/L).
One site (Waitanguru) was slightly elevated (0.012 mg/L), which can contribute to problematic plant and algae growth if levels stay high.Suspended Sediment / Water Clarity:
Three sites (20%) had Excellent water clarity (A band).
One site (Waitanguru stream) had Fair water clarity (C band).
Nearly three quarters of all sites (73%) had Poor water clarity (D band).
Water clarity bands for each site are based on the National Bottom Line (NBL), which varies depending on local landscape characteristics (e.g. geology, climate, and elevation). For Mokau River sites, the NBL is either 1.34 m or 0.61 m, depending on location.
[1] Drinking water for livestock should contain < 100 cfu/100 mL (median value) of E. coli. Livestock Drinking Water Guidelines (2023), Australian & New Zealand Guidelines for Fresh & Marine Water Quality.
2025 Quarterly Summaries
November 2025
Water quality was Good in Waitanguru stream (Site 10), and Poor in Mangaotaki river (Site 11) and Kihikihi stream (Site 30).
E. coli concentrations were low in Waitanguru stream (190 cells per 100 mL), falling within health guidelines for swimming (540 cells per 100 mL). Concentrations were elevated in Mangaotaki river and Kihikihi stream (730 to 920 cells per 100 mL), exceeding swimming guidelines.
Nitrogen: Nitrate concentrations were slightly elevated across all sites (0.53 – 0.76 mg/L) but fell well below ecological toxicity levels (2.4 mg/L). Ammonia concentrations were very low across all sites (< 0.005 mg/L). Dissolved inorganic nitrogen (DIN) was slightly elevated across all sites, exceeding the ecological impact threshold (0.5 mg/L).
Phosphorus: Dissolved reactive phosphorus (DRP) concentrations were low across all sites (≤ 0.008 mg/L).
Suspended sediment: Water clarity was Excellent in Waitanguru stream (3.15 m) and Poor in Mangaotaki river (0.90 m) and Kihikihi stream (0.89 m), relative to the national bottom line (1.34 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: 12th November 2025
Mokau River – Summary of water quality collected from 15 sites across the Mokau River catchment on 12th November 2025
Water quality was Fair across the Mokau River Catchment. While most sites had low to moderate levels of nitrogen and phosphorus, 73% of all sites had poor water clarity and 60% had elevated E. coli concentrations. The sites with the best water quality in the Mokau River catchment were Whareroa stream, Ramaroa stream, and Waitanguru stream.
E. coli (Microbial Contamination):
Three sites (20%) had low concentrations (≤ 190 cells per 100 mL), a low risk for swimming.
Two sites had very low concentrations (< 100), considered safe for livestock drinking water[1].
Another three sites (20%) had slightly elevated concentrations (350 - 400 cells per 100 mL)
Just under two thirds of sites (60%) had very high concentrations (610 – 2,200), which exceeded recommended levels for swimming.
Nitrogen
Nitrate:
Two thirds of sites (67%) had low concentrations (≤ 0.48 mg/L) and a third of sites exceeded this ecological impact threshold (> 0.5 mg/L), which may affect stream health.
All sites fell well below ecological toxicity thresholds (2.4 mg/L) for native fish and invertebrates.Ammonia:
Most sites had low concentrations (<0.005 - 0.03 mg/L), of little concern for aquatic life.
Two sites had slightly elevated concentrations (> 0.03 mg/L), which can impact sensitive aquatic species.Dissolved Inorganic Nitrogen (DIN):
Two thirds of sites (67%) had low concentrations (≤ 0.50 mg/L).
The other third had slightly elevated concentrations (0.53 – 0.77 mg/L), exceeding the ecological impact threshold of 0.5 mg/L.
Phosphorus
Dissolved Reactive Phosphorus (DRP):
Two thirds of sites (67%) had low concentrations (0.003 - 0.01 mg/L).
The other third of sites had slightly elevated concentrations (0.011 – 0.013 mg/L), which can contribute to problematic plant and algae growth if levels stay high.
Suspended Sediment / Water Clarity:
Three sites (20%) had Excellent water clarity (A band).
One site had Fair water clarity (C band).
Nearly three quarters of all sites (73%) had Poor water clarity (D band).
Water clarity bands for each site are based on the National Bottom Line (NBL), which varies depending on local landscape characteristics (e.g. geology, climate, and elevation). For Mokau River sites, the NBL is either 1.34 m or 0.61 m, depending on location.
[1] Drinking water for livestock should contain < 100 cfu/100 mL (median value) of E. coli. Livestock Drinking Water Guidelines (2023), Australian & New Zealand Guidelines for Fresh & Marine Water Quality.
Mangaotaki Mairoa
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.
Mōkau River has signs of ecological stress.
Freshwater invertebrate MCI scores indicate ecological stress at some sites in all sub-catchments expect for Mokauiti-Aria, where nearly all sites had good MCI scores and two out of three sites had good fish scores. Mangaotaki-Mairoa also had two sites with good invertebrate scores.
The number of insect species detected from eDNA (an indicator for ecological health) were low to moderate, ranging between 20 to 40 species across the 7 sub-catchments. Mapiu stream, Mapara stream, Mangaotaki and Mokauiti streams had the highest number of insect species, while Mangaokowhai stream and the Upper Mōkau had the lowest number of insect species detected.
Native freshwater mussels, a rare invertebrate species and filter feeder, were detected in the sub-catchments of upper Mōkau, Mokauiti-Aria and the lower Mōkau.
The Mōkau river has a diverse fish community in the lower reaches (14 species), however, fish diversity is very low in the mid and upper reaches, consisting mainly of eels (longfin and shortfin) and brown trout.
Only one whitebait species was detected, Īnanga, in the lower reaches only.
Threatened fish species detected in the catchment include, lamprey, Īnanga, redfin bully, longfin eel and torrentfish.
Four species of introduced fish detected, mosquito fish, goldfish, brown trout and rainbow trout.
Barriers to fish migration in the Mōkau river, including manmade structures like dams and perched culverts and natural features like high waterfalls, will be restricting fish diversity.
The Mōkau River has at least two large manmade barriers to fish migration, the Mokauiti Dam and the Wairere Dam, and at least on large natural barrier, Omaru falls (45m high).
Many of our native species are excellent climbers, elvers can scale waterfalls up to 40 m high and kōaro even higher than this.