Understanding fish passage - FAQs

There are just over 50 freshwater fish species native to New Zealand. Three-quarters of these are classified as at risk or threatened with extinction. 

Many of our iconic native fishes, such as eels (tuna) and whitebait, migrate between the sea and our rivers. As the small, finger-sized juveniles make their way upstream to reach the habitats they need to grow, feed and breed, they increasingly encounter man-made barriers such as dams, culverts and weirs. 

Fragmentation of river systems is a key driver in their decline. If they can’t get past these obstacles, they are not able to access the essential habitats required to complete their life cycle. 

New Zealand has some of the highest densities of barriers to fish passage in the world – on average individuals can encounter a barrier every 6.5 km on their journey upstream. Nearly half of New Zealand’s rivers and streams are already partially or fully inaccessible to migratory fish. NIWA research, tools and guides are supporting councils, kaitiaki, community groups, rural professionals and landowners as they endeavour to fix those structures so more rivers are accessible.

All fish move around as they seek out food, refuge and places to breed. Barriers in waterways impede or block these movements, reducing the distribution and abundance of many of our fishes. Some species (e.g. eels, galaxiids, torrentfish, smelt, lamprey and bullies) also undertake longer migrations, spending time both at sea and in river habitats. These movements make these species particularly vulnerable to barriers such as dams, weirs, falls, tide gates, culverts, screens and high water velocities that hinder their movements.

Juvenile eels and some galaxiids (giant, banded, and shortjaw kōkopu and kōaro) are good climbers and can ascend near vertical wet rock faces and falls of up to 15 m high. Consequently, they are more able to bypass some barriers compared to species such as smelt, inanga and mullet that cannot climb.

Providing fish passage is good for most native fish and freshwater species (including trout), but removing barriers can have an impact by introducing invasive species to a new area. Some important locations need barriers to help protect native species and ecosystems by keeping invasive fish (including trout) out.

Effective fish passage connects all the habitats that are necessary for freshwater fish and other instream organisms like kākahi, shrimps and aquatic invertebrates, to complete their life cycles. Ensuring fish and other organisms can move within, over and through physical structures, as well as managing the water quality and flow conditions in a waterway that may impede passage, are essential for fish passage management. Continued research and the development of assessment tools and design guides is vital for these threatened freshwater taonga.

NIWA research has informed development of the New Zealand Fish Passage Guidelines that in turn were used to inform new regulations in the National Policy Statement for Freshwater Management and the National Environmental Standards for Freshwater. These regulations mean any new structure that is put across a river or stream now needs to be designed to enable fish to get past. There are also requirements to provide and maintain fish passage in the Freshwater Fisheries Regulations (for more details see Fish passage authorisations: Apply for permits [DOC]) and in regional plans.

A rock ramp fishway is a rock structure that can be built to help fish overcome vertical drops, for example at the downstream end of culverts or below weirs. It effectively acts as a fish staircase that helps fish to get up and over a barrier.

Koen Beets, WCRC

Attribution, Non-Commercial, No Derivative Work

Koen Beets, WCRC

Attribution, Non-Commercial, No Derivative Work