WATER QUALITY

WATER QUALITY

KOI CARP were a far bigger problem in relation to water quality, than farming operations. If we stopped all farming in the Lake Waikare-Whangamarino catchment completely, we would still not achieve the water quality targets due to the effects of Koi Carp.

To effectively eradicate Koi Carp we would need to have a safe biological method of control as that would be the only way to achieve the complete eradication from all waterways within NZ.

But in saying that we can’t just ignore the problem because we don’t currently have an adequate biological control available. We need to take action to physically control the spread of Koi Carp and keep the biomass down to a level where we can protect our native biodiversity from extinction.

Fact:  Koi Carp are designated as an unwanted organism and a noxious species.

Fact:  Koi Carp are very successful breeders in New Zealand with each adult female producing 100,000 eggs per kilo of body weight.

Fact:  Koi carp cause habitat loss for plants, native fish, invertebrates and waterfowl¹¹ and as they gather for spawning¹² or feeding in the shallow margins of the waterways, Koi biomass can reach 4000 kg/ha.

Fact:  ⁷Koi Carp cause erosion of river and pond banks and destroy habitat for native fish and waterfowl and they significantly increase water turbidity. They are highly tolerant of poor water quality – surviving well in degraded water and contributing to the decline.

Koi Carp are one of the most rapidly multiplying invasive pests that have been released into the New Zealand environment.

To have any chance of success in addressing the desired improvements in water quality then we “MUST” put in place strategies to deal with the invasive pest fish species such as Koi Carp.

Failure to address the pest fish issues will result in absolute failure of the ability to achieve the requirements of the NPS on Fresh Water Quality.

The water will be too sediment laden for swimming and there will be no native flora or fauna left for food gathering after the Koi Carp have finished feeding. Koi carp are a serious threat to our waterway’s biodiversity.

Koi Carp are creating huge problems with erosion of waterway margins in all areas where they are established and this has the potential to affect the rural water control structures such as the river stopbanks, drainage control gates etc. This erosion is also causing huge problems for farmers with undermining of fences allowing stock access to waterways and the associated costs of repairs to such fencing.

Surveys undertaken for Waikato Regional Council have shown that koi make up 80-90 per cent of the biomass of some waterways.

Koi Carp are not as visible in the wild as possums, rabbits, feral goats etc. but we believe that they are the number one problem facing our native biodiversity by some considerable margin.

Koi Carp with their breeding rates and lack of any reliable predators in the New Zealand waterways are effectively the rabbits of our waterways.

Aside from the issues around native biodiversity they are also going to have a huge effect in the future on our supply of potable fresh water.

It is not good enough, (to say that we can’t eradicate them and because we are not sure what to do or who will do it and how we will fund it) to sit on our hands while the problem is growing exponentially. We need to take action now.

We need to ensure action is taken immediately, by those departments that have responsibility for managing native biodiversity and controlling exotic pests.

Blaming landowners for causing the majority of the degraded water quality as currently seems to be the fall-back position is not justified by monitoring result.

The catchment landowners are spending thousands fencing and riparian planting on their properties and even in the upper areas of the catchment too; So DOC, and other agencies which are charged with controlling parts of the catchment need to stop blaming others for not doing their job, and start taking action to control the explosion of Koi Carp in their areas of responsibility.

In the report from a study carried out by Dr D C Edmeades and Mr F Phillips on behalf of the Primary Stakeholders Catchment Trust in 2017, they stated the following:

1. 26. The water clarity is lower and the phosphate concentration is higher at the Whangamarino (Island Road) site than in the upper reaches of the catchment suggesting that some process within the wetland is enriching the water in sediment and phosphorus. This is consistent with koi carp activity.

1. 27. The wetland appears to attenuate the E.coli loadings from the sub-catchments.

1. 28. The total P load discharged at Island Road is about 32 tonnes/year of which 21% is derived from the Matahura sub-catchment and 14% from the catchment above Jefferies Road. 

1. 29. Thus the two predominantly farming catchments (above the Jefferies Road and the Matahura sites) contribute about 35% of the P load leaving Whangamarino Island Road site. By difference about 65% is coming from Lake Waikare and the Whangamarino Wetland

CONCLUSIONS: WATER QUALITY

Notwithstanding the limitations in the data, several conclusions can be drawn from this analysis: 

1. 32. In terms of water quality, the sediments and phosphorus are the twin limitations. This conclusion is consistent with a) the trends in the water quality data b) the actual current water quality data and c) the P loading calculations.

1. 33. The P concentrations and the sediment loadings in water are linked because most of the P in waterbodies is particulate P (i.e. attached to soil particles). For this reason the same mitigation options apply to both contaminants.
2. 34. The two contaminants nitrogen and pathogens (e-coli) are not of major concern in this catchment.

1. 35. From the information available at present the single dominant proportion of the P and sediment coming from this catchment is from the Waikere Lake and the Whangamarino Wetland.  This suggests that the biggest single ‘lever’ for managing water quality in this catchment is modifying their management in situ. 

Given the results of their study and with the large body of knowledge available in regard to the spread and total biomass of Koi Carp in the Lower Waikato Region, it is reasonable to assume that a majority of the sediment problems are occurring in the Whangamarino Wetland and Lake Waikare and caused or at very least exacerbated by the effects from Koi Carp.

Whilst the Lake Waikare Monitoring Plan will add to the knowledge of sediment deposition within and coming from the Lake, it is imperative that action be taken a.s.a.p. to control Koi Carp.

The Landowner stakeholders in the catchment have made many improvements to their operations as time has gone by to mitigate the effects of their farming operations on the local environment and this is an ongoing action for them, yet we ignore the effects of Koi Carp even though they are in the waterways and breeding like rabbits or worse. Every day the problem of Koi Carp is growing and as seen in the results of the study and as discussed, they are most likely to be the major cause of sediment deposition and the elevated levels of Phosphorous occurring mainly within the Whangamarino Wetland.