The problem with freshwater pests
Koi are pest fish
Freshwater pests include waterweeds, pest fish, and the invasive alga didymo.
These introduced species cause enormous damage to our unique freshwater habitats and diminish our recreational opportunities.
Freshwater weeds can also have adverse economic impacts including clogging dams and drains, and reducing suitable habitat for eel and whitebait.
Once freshwater pests become established, they are difficult and costly to control.
Didymo is an invasive alga
If we can prevent them getting into our waterways in the first place we have a better chance at stopping their spread.
You can help stop the spread
Protect our waters from freshwater pests.
- Drainage and machinery contractor - ensure any weed is removed from machinery before moving to other water-bodies and waterways.
- Fisherman or eeler - remove all fragments of weed from nets, fishing equipment and waders before you leave the area. Salt bath and/or bleach fishing nets.
- Boat operator - check boats, motors, trailers and anchor lockers for tag-along weeds immediately on removal of equipment from the water.
- Aquarium owner - don’t dispose of aquarium contents into or near a waterway.
- Trampers and hunters - check dogs, boots and boats for weed before you leave the area.
- Landowner - don’t allow drainage equipment, eel nets or boats into water bodies on your property unless they are free of weeds.
Check, Clean and Dry between waterways
Clean, Check, Dry to help prevent the spread of didymo and other freshwater pests
Check, Clean and Dry all boats and recreational equipment between waterways.
Freshwater pests (including waterweeds, pest fish, the eggs and fry of pest fish, and the invasive alga didymo) can 'hitch a lift' on boating and recreational equipment and start new pest infestations.
In damp conditions freshwater weeds can survive out of water for long periods. Therefore they can be spread even if you do not use your equipment regularly.
Checking, Cleaning and Drying boats, trailers, jet units and fishing equipment helps to prevent the spread of freshwater pests between waterways.
Do not move plants and fish between waterways
The best way to prevent the spread of pest fish and waterweeds is to not move them between waterways. If you do want to move them between waterways, permits are required.
DOC does not require permits for possession or transfer of native freshwater species if your pond or aquarium is indoors, undercover or prevented from overflowing into natural waterways. Source your water plants and fish from reputable pet shops and garden centres.
If you want to move any freshwater plants or animals between waterways, contact your local DOC office for more information. Depending on the species and activity you want to do, you may need permits from the following agencies; Department of Conservation, Ministry of Fisheries, Fish and Game New Zealand, Ministry for Primary Industries. There are fines if you do not have the right permits.
Do not release plants and fish into waterways
Dispose of aquarium contents appropriately. Compost waterweed and return fish to pet shops for re-homing.
Report an unusual freshwater plant
Note the location and take a sample of the plant if possible. Inform your local DOC office or your Regional Council Pest Plants Officer as soon as possible.
Current concerns
Freshwater pests have dramatically expanded their range in recent years. Of particular concern has been the discovery of the waterweed hornwort, and the pest fish species koi carp and Gambusia in the South Island for the first time. DOC has been involved in eradication programmes to remove these species to prevent them becoming established in the South Island.
