Two of the invasive weeds in Lake Rotorua - Egeria densa with a single stem of Lagarosiphon major. Photo:
The Department of Conservation (DOC) and West Coast Regional Council are urging boaties, anglers and anyone who spends time on West Coast lakes to help protect against freshwater pests.
DOC Hokitika operations manager Owen Kilgour said some pests, such as lindavia, lake snow, could not be seen by the naked eye and a single drop of water, plant fragment or fish egg could be all it took to spread an invasive freshwater pest from a contaminated waterbody.
Pests to look out for include gambusia or mosquito fish, rudd, koi carp, oxygen and parrot's feather.
"We all need to do our bit and protect our lakes by always checking, cleaning and drying gear that's been in contact with water before moving on."
Kilgour said early detection was essential to managing new incursions and preserving lake quality.
Freshwater pests that get into lakes squeeze out native freshwater vegetation and fish.
Weeds such as lagarosiphon are bad for water quality and reduce dissolved oxygen, which affects native species and sports fish habitats.
Where freshwater weeds grow in waterways and drains, they exacerbate flooding in the surrounding catchment. Both pest fish and weedy plants are extremely difficult and expensive to get rid of once established.
West Coast Regional Council biosecurity coordinator Taylor Blyth said each summer a number of lakes were selected for surveillance based on incursion risk and previous surveillance history.
He said the weeds causing the biggest concerns were lagarosiphon major, and egeria densa.
"Lagarosiphon is already in Lakes Paringa and Ianthe and the Kapitea Reservoir. Egeria is known to occupy two sites within the region."
The council is using environmental DNA as part of its surveillance in a bid to catch new incursions, but checks were only done annually, so Blyth said it was not a silver bullet - and the most effective approach was to stop weeds from spreading by cleaning equipment.
Blyth said jet boaters visiting the Coast from Canterbury or Central Otago could potentially spread freshwater pests to every waterbody they visit.
The next step in the surveillance programme is to do an intensive grid search in late spring.
Discoveries of any freshwater pest should be reported via the Find a Pest or iNaturalist apps. People can also contact WCRC directly by emailing clear photographs and coordinates to info@wcrc.govt.nz.