Fact: Koi Carp are designated as an unwanted organism and a noxious species. They are very successful breeders in New Zealand conditions and cause habitat loss for plants, native fish, invertebrates and waterfowl.
Koi females produce approximately 100 000 eggs per kg of body weight. A typical female can produce 300 000 eggs annually (or more if they spawn11 more than once). Koi carp spawn throughout the summer. As they gather for spawning12 or feeding in the shallow margins of wetlands, rivers and waterways, koi biomass can reach 4000 kg/ha.
They eat a wide range of food, including insects, fish eggs, juvenile fish of other species and a diverse range of plants and other organic matter. They feed like a vacuum cleaner, sucking up everything and blowing out what isn’t wanted and they burrow away at the banks causing erosion7 as well, which all contributes to poor water quality.
Once established in an area they have a huge detrimental impact on rivers and ponds; they significantly increase water turbidity. Once introduced they quickly become the dominant fish in water bodies.
Koi carp are widespread in Auckland and Waikato. (The population has exploded, and they now make up 80% of the total biomass3 in the lower Waikato river catchment. It has been estimated that there are approximately 500,000 tonnes of Koi Carp in the lower Waikato Catchment).
Many people are unaware of the damage done to our waterways by pest fish. Unfortunately Koi Carp have spread into the wild, become pests and are threatening New Zealand’s freshwater species and environments.
Even if we were to ban farming totally we would still have a problem with water quality from the effects of the invasive pest fish species, but they have been largely ignored with the focus for water quality improvement being almost totally on the effects from agriculture.
This is where the STUPIDITY comes in.
Koi Carp is rapidly becoming one of the worst invasive pests in New Zealand (the equivalent of the Possum/Rabbit in the waterways) and they are a national problem which requires a national solution to allow control measures to be implemented across the whole country.
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, as failure to do so will result in absolute failure of the ability to achieve a reasonable level of 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.
We have spent millions of dollars of both Taxpayers and Ratepayers money in researching Koi Carp in the New Zealand environment and identifying the damages they cause to our native flora and fauna yet we have done almost nothing to either control or eradicate them from our waterways!
STUPIDITY!!!!
If all of the money that has been spent had been put towards paying a bounty on dead Koi Carp, how many would have been removed from the waterways?
Even at a dollar a fish (which sounds very high) we would have seen millions of Koi removed but no here we are in 2025 still discussing what can be done to deal with a pest fish that has been known about since the early 1980’s.
Nearly fifty years and we still haven’t seen one effective strategy put in place to try to either control or eradicate them. But we have kept a lot of people employed in talking about them.
Apart from research projects and one Iwi group, the only thing that has actually been done is; to help stop their spread, a containment area between Auckland and Hamilton was created. In the containment area, recreational fishing was permitted, but all koi had to be killed when caught.
Since the containment area was designated they have spread far past Hamilton and have now been found in the Waikato River up-stream of the Karapiro dam. They are spreading whether naturally or with human assistance we don’t know but we do know that they have spread outside the containment area.
If koi reach the Rotorua or Taupo lakes (and I believe it is a case of when not if), it would devastate our internationally renowned trout fisheries. People must realise that koi are not only a serious threat to our waterway’s biodiversity they will rapidly become a real threat to our freshwater fishing tourism industry and also our national economy.
Tawera Nikau and his Iwi are involved in catching and killing Koi Carp with some backing from the Ministry for the Environment. They process the fish in their facility at Hampton Downs and there is no by products. They are producing fish bait and berley with anything left after this process being turned into agricultural fertilisers. The only other ones currently actually catching Koi Carp are the bowhunters who hold an annual competition for catching carp and they extract approximately 5 tonnes each time which are then ground up.
The problem is that given the rate at which Koi breed and multiply these methods don’t even really scratch the surface of the problem.
Mr Jeffrey To from Houston Technology Group has been working hard developing an autonimous robotic electronic fishing method which is able to selectively target Koi Carp using visual indentification and release other native fish bycatch. He has been trying to get assistance from other organisations to further his development work but without any success so far.
To the best of my knowledge this is the only other method being actively developed to target Koi Carp and which I believe has an extremely positive outlook for success.
Currently there is a proposal under Plan Change 1 in the Waikato Regional Council area of control to target agricultural industries and in the Whangamarino/ Lake Waikare catchment they are going top require all farming operations to obtain a discretionary consent to allow them to carry on farming.
It has been suggested that in this catchment under PC1 there will be a reduction required in dairying (approx 12%) and sheep & beef (approx 39%) with no cropping or forestry allowed at all. In this catchment alone this is going to see a huge reduction in the local job market, economy and associated rural service industries alongside a drastic reduction in rating income for both Regional and District Councils.
So much for the coalition governments desire to double the agricultural production and boost our national economy.
Prior to 2020Local Government New Zealand commissioned a report on the impact of the new rules for Fresh Water Management on the Waikato region, and the end result of the implementation according to that report was that 68% of Sheep & Beef farmers and 13% of Dairy farmers would leave the agricultural sector.
The report suggested that these farmers will be replaced by forestry operations and even if that were true (I personally disagree) the effect on the small rural communities from this gutting of the farming industries will just result in more rural ghost towns.
MfE’s predictions at that time were that meeting new freshwater regulations would cost landowners $900 million and another $140m a year in annual compliance costs and loss of profits.
Yet the WRC in their initial costing of the implementation of PC1 which has virtually the same rules, predicted that the cost to the agricultural sector in the Waikato region alone would be $500 to $600 million dollars per year for the eighty year time frame of the proposed plan change implementation.
Add PC1 and the problems that come with Koi Carp and it is obvious that our economy cannot withstand the effects from both of these problems. You cannot regulate stupidity and expect common sense as the outcome. We are staring at financial and environmental bankruptcy from these two issues.
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By Andy Loader, Poke the Bear