A new management plan is being developed for South Canterbury hydro lakes Waitaki and Aviemore after large infestations of the invasive lake weed lagarosiphon were found.
The infestations were found by divers surveying the lakes as part of regular monitoring and control work funded by Toitū Te Whenua Land Information New Zealand (LINZ), Meridian Energy and Environment Canterbury (ECan).
Both lakes have been considered largely weed-free, with only small areas of weeds previously found in Lake Aviemore.
LINZ Biosecurity Manager Tracey Burton says the discoveries in March come as a blow after 15 years of efforts to protect the lakes from lagarosiphon.
“We were always working against the flow to keep this weed from spreading downstream from its stronghold in the Ahuriri Arm of Lake Benmore. But our combined efforts allowed us to hold the line, keeping these lakes weed-free until now.”
Burton says the new infestation in Lake Waitaki is particularly large at 750 meters long – equivalent to 15 lengths of an Olympic sized swimming pool.
“This shows just how quickly lagarosiphon can take hold in new habitats. All it takes for new plants to establish is a tiny fragment transferred downstream, by boat, fishing gear, or natural flow through the lake system.”
Burton says the goal was to eradicate the weed from Lake Aviemore and keep Lake Waitaki weed-free, but this is no longer achievable.
“Unfortunately, the size of these infestations means we will now have to change tack and do our best to manage lagarosiphon in these lakes and prevent it from spreading into other weed-free waterbodies.
“Now the weed is in these lakes it’s more important than ever that lake users check, clean and dry all gear when moving between waterways.
“It’s essential we all do our bit to stop the spread of lagarosiphon as left unchecked it can very quickly take over and choke waterways, smother native plants and have a big impact on how we use and enjoy our lakes.“
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