You never know what dangerous pest plant might turn up quietly in your neighbourhood or even your own backyard.

A recent example of a surprising find was the discovery in Waipa district of the highly invasive aquatic pest plant salvinia, which can grow very quickly and choke waterways. People are required to notify the Ministry for Primary Industries or Waikato Regional Council if they find it.

The Waipa find last month was made by a Waipa District Council officer at a storm water pond near Te Awamutu.

He noticed a small amount of the plant in the pond but didn’t think much of it as it was just another pond weed. But when he went back six weeks later the entire pond had filled up with what was subsequently identified as salvinia.

“In six weeks it had gone from pretty much nothing to the entire 50 metres by 20 metres pond,” said regional council biosecurity officer Darion Embling, in a statement to mark Biosecurity Month.

“That shows just how quickly salvinia can multiply and take hold if it isn’t identified and dealt with promptly. It’s an example of really good vigilance by the Waipa district staff member.”

Salvinia quickly forms extensive floating mats on still waters and swamps, smothering waterways and badly affecting water quality. It can double in area within 10 days.

Mats of salvinia kill off native plants, attract mosquitoes, block dams and irrigation systems, remove oxygen from the water and create a a water hazard for people and animals.

The source of salvinia, a native to Brazil which has been in New Zealand for some years, is generally by accidental distribution within the aquarium trade and ends up in small backyard ponds.

The Ministry for Primary Industries and its biosecurity contractor will be managing the removal of the Waipa find.

Mr Embling said other tips to prevent aquatic weeds coming into New Zealand include:

• be careful what you buy over the internet
• understand what is banned from sale and distribution.

Also, keep an eye on plants that appear in ponds and, if it looks invasive, call the regional council on 0800 BIOSECURITY (0800 246 732).