Wetlands & Volume of Water Available to Eels

“You let water get to the sea?” 

A visitor to New Zealand was recently heard to say.  He genuinely felt that this was wasteful and that it would be better completely used for agri-business.  


Our own government have expressed the view that we waste too much water!

We suspect most New Zealanders have a very different take on our rivers. 


Wetlands and Water management

New Zealand is an island nation. Its rivers are characteristically quite short and relative to continental rivers, fast flowing.

Unlike the South islands Southern Alps, the North Island has no major mountain range running it’s full length. As a result its rainfall patterns are quite different and it has no significant snowfields to store water from winter into summer. 

Apart from some areas of the south East, rainfall is usually quite moderate and reliable throughout the year.    


It is often said that “NZ has plenty of water”. It is more correct to say that NZ gets plenty of rain. It is how we manage that rain that determines whether we have plenty of water, or not.   

In pre European days the North Island was characterised by extensive swamps and meandering lowland rivers and streams. In other words plenty of water, and ideal habitat for native fish like eels.

With the advent of intensive agriculture and advances in mechanical technology  these swamps were soon drained and meandering rivers and streams were straightened. Rainfall that was once retained in wetlands and made its way slowly to the sea, now has no retention and an expressway to the sea.

In the same time frame, demand for the use of water for farming, factories and people was rapidly increasing and continues to do so.

In Waipa District Council a recent survey found that over 98% of wetlands had been drained. This would be fairly typical of most of the country. So in a quite short space of time we have gone from having ‘plenty of water’ to a situation where we have demand beginning to exceed supply.

Given a rapidly increasing population  (net migration gain of 72 000 in the 12 months prior to May 2017) then demand for water will continue to rise rapidly.To meet the needs of this population growth and the needs of freshwater fish, like eels, a new set of water management objectives need to be set.

Water retention in terms of, quantity, quality. and continuity need to be  fundamental objectives of on land/farm management.

Wetlands are the first structure required as they serve multiple benefits. They slow runoff during rainfall events trapping  soils, sediments and farm effluent. They give time for rain to soak into the underground aquifer  and release water downstream over a  long time period. When dry they rapidly absorb large amounts of water and decrease the severity of peak river flows.They provide habitats for a very wide range of wildlife. Wetlands need to be a standard fixture of modern farming practice and land management.

Damming of water is the next step in retention. Lake Taupo is our largest natural dam and is used to regulate flow down the Waikato river allowing for much higher summer flows and lower peak flows than would otherwise be the case. The hydro dams on the river also act to retain water and trap sediments making for much cleaner water below Karapiro dam. However the greatest gains are to be made by the installation of many smaller dams on farms and land  to retain water and entrap sediments and pollutants. Dams should be a standard fixture of modern farming /land practice.   


Regional Councils are the principal managers of rivers and streams (rather than individual land owners). Despite a rapidly growing public concern at the state of our waterways and water and wildlife, Regional council waterway management practices have not changed for at least the last 50 years. They remain fixated with ‘getting rid of water’. To elaborate, getting rain from the mountains to the sea as quickly as possible with as little flooding as possible.

No regard is given to fisheries or wildlife or impacts on the marine environment. 

To ensure a healthy freshwater environment into the future  Regional councils need to  manage rivers and streams to suit a much wider range of objectives, one that includes fisheries. 

Whilst it is blindly obvious that eels need water to live, it is also important to remember that they need sufficient water every day of the year.   As we all know, rainfall is mightily variable and droughts are often experienced over summer months.  Anybody wanting more information about flow could refer to their Regional Council websites.  Horizon’s have an excellent report:  Statistical Analysis of River Flow Data in Horizon’s region. 

In pre-colonial days:

  • water was not taken in huge quantities for irrigation

  • there were no engineers channelising rivers to convey water more quickly to the coast

  • Extensive wetlands acted as a buffer retaining water and releasing it slowly. 

  • There were no flood control systems pumping water and eels (in pieces) out of pasture back into the rivers.

  • There were no great cities taking the water out of rivers for human domestic supply.

  • Complexes of hydroelectric dams did not change flows to suit consumption convenience

We at EECo accept that our economy and society is centred around utilisation of water. 

We also believe that the country especially national and local government is becoming more aware of the issues surrounding our use of fresh water resources. 

Some farmers and industrial concerns are doing exemplary work to mitigate the effects of water abstraction and use.

We are, however, nervous that the level of water take in some catchments is nearing or already exceeding prudent levels and that minimum summer flows are being breached! 

Wetlands in the North Island have been reduced to 10% of their original extent although there is a growing trend of re-construction with is heartening.


Wetlands are incredibly important areas of eel habitat as they provide all the benefits that eels need to live – shelter, slow flow and abundant food.


Wetlands also act as a buffer after flood events releasing the excess water slowly causing less damage downstream and reduced siltation.


How would you like to live in this?


How would you like to live in this?

Some ways to mitigate these issues are:

  • Water storage reservoirs filled at higher rainfall periods to supplement summer or low rainfall requirements

  • Well planned riparian planting    

  • Continue to re-establish wetlands

  • Continue the excellent trend of including ponds in civic construction projects, including roading.

  • Robust regimes for those who control river flow

  • Perhaps, most importantly, a more robust system for consenting water uptake