Ngā riha wai

Aquatic pests

Gisborne is home to many waterways which are at risk of becoming contaminated with freshwater pests and weeds.

Keep our waterway clear of aquatic pest plans, fish and algae by adopting the 'Check Clean Dry' method before leaving a waterway.


Gisborne district is free from Didymosphenia geminata, common name didymo or rock snot - and we need to keep it that way.

Didymo is an invasive freshwater alga that grows in rivers, streams and lakes.  Didymo continues to devastate many rivers in the South Island, where it favours cold, clear, shallow running water.

If you suspect you've sighted didymo or anything unusual, contact us or Biosecurity NZ's hotline ph 0800 80 99 66.  
Try to record the location, take a photo if you can, but please don't try to remove it yourself.

Didymo can be spread by just one microscopic algal cell in a single drop of water.

Even if you can't see it you could easily spread it.

It's believed didymo has not yet reached the North Island, but if it does, it could cause significant damage to fresh water native fish, trout, plants and insects in our region.

It makes rivers, streams and lakes unsightly and most unpleasant for swimming, boating and fishing.

We all need to be extremely careful when going from one waterway to another.

Water users are legally obliged to prevent the spreading of didymo.

Didymo can form large mats on the bottom of lakes, rivers and streams which have a smothering effect on rocks, submerged plants and other materials. This can affect stream habitats and sources of food for fish and make recreational activities like kayaking, fishing, boating and swimming unpleasant.

Didymo is native to temperate northern hemisphere areas. Until didymo was found in the lower Waiau River of the South Island in 2004 it had not previously entered the southern hemisphere.

The 'Check Clean Dry' method to contain freshwater pests

'Check clean dry' has been adopted to prevent didymo and freshwater pests infecting Gisborne's waterways.

When leaving a waterway ‘check’ for and remove any visible clumps from gear, leave it at the site or in a rubbish bin.
‘Clean’ your gear - use 5% dishwashing liquid or nappy cleaner or 2% bleach, soak for at least 1 minute.
If items are not cleaned, they need to be completely 'touch dry’ for at least 48 hours before entering another waterway.

Go to Ministry for Primary Industries' website for recommended cleaning methods.

Freshwater weed pests

We need to keep freshwater weeds out of our waterways. If you see anything change or unusual about a waterbody, please let us know.

Take a note of the location, and take a photo if you can - contact Council's biosecurity team or the Department of Conservation

Weed pests to keep an eye out for

    • Lagarosiphon
    • Hornwort
    • Alligator weed
    • Water Hyacinth
    • Hydrilla

Niwa Report - Vegetation Survey of Aquatic and Wetland Sites in Gisborne District PDF, 7010.47 KB



Lagarosiphon is an invasive introduced freshwater weed. It grows quickly in depths of 2-4 metres. The weed is currently in Lake Waikaremoana but is actively controlled by the Department of Conservation.
Please don't dump this plant from your aquarium or pond into any waterway.



Hornwort is a freshwater perennial weed. It's widely established in the North Island, but currently contained in the Gisborne district. Hornort can grow to depths of 14 metres and without roots it can attach itself to muddy substrates.


Alligator weed

Alligator weed is a perennial herb with floating stems that can form dense floating mats. Flowers through summer, with small white clover like florets. We list Alligator weed as an exclusion pest, not yet established here. Let’s keep it that way.


Water Hyacinth

Water Hyacinth for free floating mats of shiny round leaved and distinctive mauve-blue flowers. With thick masses of roots, water hyacinth can strip oxygen from the water, killing other native plants. The matting quality means this plant can block drains and pose a danger to swimming animals and people.



Hydrilla is an exotic freshwater weed, recognised as the world’s worst submerged weed. It has been located in 4 lakes in Hawkes Bay. Please help to keep it out of Gisborne district.

For more information on weed pests visit Department of Conservation's website.

Tell us if you see these fish

If you see one of these fish or suspect you have, report it. Contact Council’s biosecurity team or Department of Conservation. Record where you found it and a photo if you can.

Pest freshwater fish

Freshwater pest fish species are not known to be in the Gisborne district and we want to keep it this way.

There's a number of pest fish species that can invade and out-compete our native fish, shellfish and destroy native habitats.

  • Catfish
  • Koi carp
  • Rudd
  • Perch
  • Tench

It's important to always remember to “Check, Clean and Dry” all gear when exiting a waterway. This included bilge water and stored water on vessels and light crafts, including kayaks and jet skis.



Catfish are best known for their distinctive whisker like barbells around the mouth, with a dark brown to green back and pail underside. They're a very tolerant species, surviving in poor water quality and will stay alive out of water for a period of time. Catfish are a predator species and will dominate native species.


Koi carp

Koi carp are a large fish up to 75cm in length. Their large head and mouth with distinctive barbells are ideal for stirring up sediments and disturbing aquatic plants. Koi carp come in a range of colour from orange, white, black and gold.



Rudd fish feed on insects, aquatic plants and other fish, out-competing native species for food and degrading native habitat. Rudd are stocky fish, growing up to 40cm in length, with distinctive orange fins. They can lay thousands of eggs at a time.



Perch are a predator species, identifiable by their 2 large dorsal fins and humped arched back. The greenish to grey fish grows up to 4kg and females are capable of producing 2,000 to 10,000 eggs depending on maturity.



Tench are an imported sports fish. Olive green colouration and can grow up to 4kg. Tench have thick fleshy fins and distinctive orange eyes.