New Zealand has an enviable reputation for her ‘pure’ environment and, mostly, this is well deserved. 

It would also be fair to say that, as a people, we are well aware of the need to protect and nurture our aquatic environment.

However, every country is bound to generate sufficient wealth to feed, shelter and create meaningful lives for their people.  This requires utilisation of available resources and, unfortunately, creates the potential for environmentally damaging activities.



The job of a whole array of agencies along with farmers, business concerns and the people is to develop rules of conduct to limit pollution to acceptable levels.  People will always differ on what might be an acceptable level and that bar will be raised with increasing wealth. 



Pollution in our waterways comes in many flavours.


Every stretch of water will have its own set of dynamics depending on the natural geology of the area, human activities upstream, pest control, riparian planting, flow, depth, temperature.

Pollutants include: 

  • Animal and human sewage in various degrees of treatment.  This is the biggie, which even if treated properly places much higher nitrate loadings in our rivers. In turn, this creates potential for algae blooms and super growth of aquatic weeds both of which are bad news for aquatic fauna including eels.
    Huge strides have been made with treatment of household waste and farm practises are on the improve.  However, this is being countered by very rapid farm intensification especially dairying.  Greater uptake of modern farm practises and superior riparian management will help.  Further intensification must be limited to acceptable levels.

  • Fertilizer run-off.  The other biggie.  The excessive use of fertilizer and poor application often results in damaging amounts ending up in waterways.
    Blue green algae blooms (pictured) can be very toxic. It will be a good day for our aquatic animals when the cost of unproductive lost fertilizer incentivises precision application protocols. 

    This is a well debated subject.

  • Siltation.  This is a normal process which has always occurred during high flow events.  However, it has now got to dangerous levels and is severely damaging shallow lakes and low level coastal lagoons. 
    Also, importantly, siltation is affecting inshore coastal fisheries including rock lobster and paua. 

    Siltation must be brought back to acceptable levels and a key tool will, yet again, be better and larger riparian margins.

  • Leaching of naturally occurring minerals particularly in geothermal areas.  This has always happened and cannot be prevented.  Levels are monitored regularly both in the animals and water.

  • Waters with elevated temperature downstream of thermal power stations & factories.  Strictly not pollution but nonetheless an anthropogenic alteration of a waterway’s ability to sustain aquatic life.  

    This is strictly controlled and monitored to acceptable levels.

  • Illegal dumping to storm water drains by households or individuals.  Most people care but, much of this issue is ignorance as to where the paint/domestic products you poured down the drain ends up and the damage caused. 

  • Registered chemicals used in the control of unwanted flora, fauna, parasites & diseases.  It is outside of the scope of this document to list these products but, some do end up in our waterways and much more work needs to be done to establish what (if any) damage they do to our aquatic flora and fauna including eels.  Again, superior and larger riparian margins along with rapid chemical breakdown helps.

  • One-off industrial point source discharges – legal and illegal.  The legal discharges have been consented and are monitored.  Illegal discharges should be reported and prosecuted.



Eels are reasonably hardy but some of the aquatic foods in their diet are not! Crustacea (including koura), molluscs and small fish species can be susceptible to even small amounts of pollutants including chemicals/nitrates, temperature and siltation.  


Eels thrive better in pastoral waterways than in the bush because of better/more food opportunities. 

  • Introduced pest fish species such as bullhead catfish and koi carp.  Apart from competing with eels for food these fish cause enormous damage to waterways by increasing suspended solids. 

    EECO along with local authorities encourage the destruction of these fish wherever they are found.

  • Exotic forestry.  This is a very important wealth generator for New Zealand but eels don’t much like the waters flowing through pine and particularly cypress plantations.  Biomass in those areas is low.  Again, along with the siltation issue, wider and better riparian margins will help our waterways and downstream users enormously.   

Good to see greater awareness of this from Councils along with drain grates enscribed with clear messages that fish are affected by stormwater.