Studies of Otago’s freshwater allow people to make up their own mind as to how clean the region’s water is Murray Neilson writes.
Duntroon dairy farmer and president of North Otago Federated Farmers, Mfanwy Alexander has accused Nigel Paragreen of Fish and Game Otago of being "a bit dramatic" in saying that Otago’s freshwater was in a "dire" state (ODT 11.3.24).
She has said that Mr Paragreen’s comments were "panicky" and "reactive". In examining what Mr Paragreen actually said, I note that he wasn’t claiming that state for Otago’s freshwaters in their entirety, but "in many parts of the region".
For it is true that Otago does have some freshwaters of very high quality — but these are largely in those parts of the region where the waters originate in native forest and high country tussock land, in the conservation estate, such as the catchments of the Dart and Rees rivers feeding Lake Wakatipu, the Makarora and Matukituki catchments feeding Lake Wanaka, the Hunter catchment feeding Lake Hawea, the upper Manuherikia above Falls Dam, and the Maclennan catchment in the Catlins district.
However, in many other parts of our region, where agricultural and urban land uses predominate, the situation is not so good.
The Manuherikia Rohe of the Clutha/Mata-Au Freshwater Management Unit (FMU) is one example.
A cursory reading of the ORC’s river water quality report for this rohe, in preparation for the Land and Water Regional Plan (LWRP), reveals that "bacterial water quality is excellent in the Manuherikia above Falls Dam, concentrations increase downstream with both Ophir and Galloway achieving band ‘D’ below the national bottom line (National Policy Statement for Freshwater Management- NPSFM )".
Bacterial water quality is below the national bottom line at all tributary sites (Hills Creek, Thomson’s Creek and the Poolburn); nutrients increase in the main-stem between Blackstone and Ophir, then DRP (dissolved reactive phosphorus) improves downstream to achieve band "B" at Galloway.
Poolburn and Thomson Creek have poor water quality across all attribute states, other than toxicity, mainly achieving band "D", below the bottom line; Dunstan Creek has degrading trends for E. coli ( human health faecal indicator bacteria) and turbidity; Ophir has an "an exceptionally unlikely" improving trend for E.coli.
The Taieri is another example. The ORC’s report on this FMU notes that water quality is "generally good, however some lower Taieri plain tributaries are degraded. Some sites here have among the poorest water quality in the Otago region. Water quality is affected by pressures such as intensive agricultural land use, urban land uses and stream modification".
The report further notes that "about half of the 22 river monitoring sites did not meet the required NPSFM standard for suspended sediment (visual clarity)".
Five sites in the lower Taieri did not meet the national standard for E.coli. Two sites, Taieri at Creamery and Owhiro Stream, did not meet the national standard for dissolved reactive phosphorus (DRP) (Excess phosphorus can cause algae growth and poor river health).
Lake Waihola usually has "C" band results for nutrients and chlorophyll-a (a measure of algae in the water).
"This result is consistent with the nutrient-enriched state of the lake, which has episodes of nutrient blooms."
Most Taieri monitoring sites recorded some degrading trends, particularly for nutrients, E.coli and turbidity, in the long term, but the 10-year trend analysis showed fewer sites with degrading trends for nutrients, and improving trends for turbidity at most sites. Lake Waihola showed degrading long-term trends for nutrients, E.coli and turbidity, although the 10-year analysis did indicate improving trends for turbidity and chlorophyll-a.
Groundwater quality monitoring also revealed that there were concerns around high nitrate concentrations and some E.coli detections in the Maniototo aquifer (groundwater can be used for domestic supply, irrigation, stock water and dairy sheds).
Some nitrate results were getting close to the NZ Drinking Water Standards maximum acceptable value (MAV) of 11.3 mg/L. (High nitrate levels in drinking water have been linked to "blue baby" syndrome).
In Mfanwy Alexander’s own area, the North Otago FMU, ORC reports that water quality "generally shows some degree of degradation" resulting from land use pressure and low flows. Aquatic insect life and E.coli failed to meet the national bottom line at about half of the monitored sites in this FMU.
The report notes that "rivers in dry catchments have less dilution and flushing capacity" and that "they are more susceptible to high nutrients and other water quality pressures associated with high-intensity land use".
Fourteen of the 16 sites monitored did not meet the required NPSFM standard for at least one measurement. The most degraded streams were the Waiareka and Oamaru Creek, which failed to meet the national bottom lines for E.coli, phosphorus and aquatic insect life.
Oamaru Creek was found to be significantly degraded, probably as a result of urban run-off.
So, readers, is water quality in some parts of Otago in a "dire" state, or is this comment merely "dramatic", "panicky" or "reactive"?
You be the judge.
- Murray Neilson is a trustee of the Clutha Fisheries Trust, a former Fish & Game councillor and a retired Department of Conservation freshwater technical support officer.
