Most likely scenario for spreading the clams originally is hitching a ride with a migrating bird - the things breed without a partner at a fearsome rate. Once in a waterway, no one anywhere has managed to eradicate them and that is the issue (along with the fact that the thing will effectively strip mine the waterways and out-compete everything else for food).
In defence of the Iwi here - do we do the usual thing and wait for someone to bowl over from the waikato with their trailer boat and drag a piece of weed with them that has a few 1mm-size spat on it straight into a fairly clean (currently) lake and infest that? There are already a couple of areas where there are invasive weed species in the lake. Or, do we take the second option - and while the size and effect of the invasive species is quantified protect the area and the only way to do it is close the door?
I dunno, I'm seeing both sides of this - Okataina is unique in it's setup and one of the 'special' NZ lakes for me, I would not want to see if infested and ecologically damaged through someone doing something ignorant.
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