A New Plymouth lake is being drained in an effort to stop invasive clams. 

Lake Rotomanu's been closed to motorised watercraft since the gold clams were found there last month, marking the first discovery of the species outside of the Waikato River. 

The lake's outlet was opened yesterday, and it will take about four days to drain completely. 

Dave Cade told Kerre Woodham it’s the worst biosecurity threat to New Zealand’s freshwater that the country’s ever faced. 

He says the clams reproduce asexually, and they’ll smother the bottom of lakes, smothering native organisms and clogging hydro stations.  

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