Stream works for fish
Riffles, pools, reaches, rapids, waterfalls, glides, eddies, meanders, overhangs and undercuts – there’s more to a stream than just water.
Rural stream
A stream on a farm in the Waitomo District. The curves in the stream are called meanders. The clearing of trees and shrubs has resulted in areas of undercut erosion.
Streams are smaller water bodies, characterised by having a current – or flow – and confined within beds and banks. Streams are part of the water cycle and also an important habitat for flora and fauna. They also play a role in breeding and migration of fish and other animals.
To learn more about some of the terms that will be encountered when looking at freshwater and freshwater fish, see Freshwater and freshwater fish – key terms.
Fish-friendly streams provide diverse habitats for our native fish as well as the insects and plants they need for food and shelter. Our native fish like to keep their cool. They’re used to shaded waterways lined with dense vegetation because over 80% of New Zealand was once forested.
To survive and complete their life cycle, native fish need suitable:
habitat type and variety
water quality (temperature, oxygen levels, clarity, pH, nutrients )
stream flow (quantity and speed)
food supply (plants and insects in the stream and on the stream margins, such as freshwater macroinvertebrates)
protection from predators
migration pathways to the sea for some species.
Focus on the water
Many stream protection works focus on the land, such as riparian restoration – planting slopes and banks to reduce erosion, creating grass filter strips to trap silt and putting up fences to keep stock from defecating (pooing) in the water or eroding the banks.
Replanting a riparian strip
Volunteers replanting a riparian strip. Reducing stock access to streams and planting native plants along the bank can change the water from murky and polluted into a crystal clear stream teeming with life.
However, for our native fish, surviving in streams can be a real challenge. Straightening, diverting or dredging streams and installing weirs and culverts can dramatically alter stream flow and destroy fish habitat and the ability of fish to migrate.
Culverts are placed in rivers and streams to enable people and stock to cross safely and easily. Weirs are built across rivers and streams to slow the flow of water and raise the level of water upstream. Both can prevent fish passage.
Perched culvert
Perched culverts – installed above the predominant waterline – are one of the most common barriers to native fish migration. Here, Hawke’s Bay Regional Council scientist Dr Andy Hicks investigates a perched culvert.
Going with the flow
Many native fish migrate between the sea and upstream habitats. For example, eels need to find their way out to sea in order to lay their eggs, and the elvers then have to return to their freshwater habitats from the ocean. Human interventions such as dams, weirs, tide gates and perched culverts are often designed so that they block the fish from passing. Perched culverts are one of the most common barriers for our native fish.
Elvers climbing a rock wall
Elvers and glass eels emerge from the water to scale the wall of a dam.
Culverts and other interventions can be designed to use the ability of elvers, young kōkopu, kōaro (collectively known at this stage as whitebait) and bullies to wriggle between stones, spend brief periods out of water and climb wet margins of waterfalls and culvert sides.
In some situations, there is no need to install fish-friendly culverts, for instance, if there is a natural barrier such as a large waterfall downstream or no suitable habitat for native fish upstream.
Culverts, ramps and baffles
Researcher Cheri van Schravendijk-Goodman discusses the problem with culverts that disconnect habitats of fish from the main river. She describes the use of fish ramps and baffles and how they help to improve connectivity between the river and tributaries – particularly for whitebait species of fish.
Barriers can also be useful tools to prevent the spread of pest fish like koi carp or to protect naturally isolated native fish like mudfish from competitors like trout.
A look at the species and habitats of your local stream will help to understand what fish-friendly culverts or pest species barriers are appropriate for your stream.
How else can we make our streams more native fish friendly?
As well as fish-friendly culverts and barriers, there are a number of measures we can carry out to assure the health of our streams and the fish and other animal and plant life that rely on them.
Excessive plant growth in waterway
Nutrients, such as phosphorus and nitrogen, carried into waterways cause excessive growth of aquatic plants. This can lead to eutrophication – the ultimate death of plants and organisms in the water.
Water quality is important to the health of fish – many fish cannot live or thrive in dirty water, such as giant kōkopu juveniles. Water quality can be enhanced by:
diverting raceway/road run-off that contains pollutants such as excess nutrients and effluent
fencing the stream to keep stock out
having a spillway for flood flows – floods often carry excess sediments into our waterways
aerating areas that suffer from constant eutrophication or toxic algae blooms.
Riprap alongside a river
Riprap is rock, concrete rubble or other material used to protect streambeds, coastlines and other waterways from scour. Scour is a form of erosion.
Fish also rely on certain habitat features within streams. These habitats can be degraded by changes in water flow, clearing of vegetation or flood events. For example, rapid flooding can carry a lot of debris and sediment that can cause scouring. Scour is the erosion of the stream bed (vertical scour) or stream banks (lateral scour) by rapid flowing water and the sediments it is carrying. Scour can also threaten fish-friendly culverts by washing away the sediment and gravel that hold the structure in place.
Culverts, ramps and baffles
Researcher Cheri van Schravendijk-Goodman discusses the problem with culverts that disconnect habitats of fish from the main river. She describes the use of fish ramps and baffles and how they help to improve connectivity between the river and tributaries – particularly for whitebait species of fish.
Fish habitats can be protected by:
rock riprap at the culvert outlet to prevent scouring
a notched rock weir or rock ramp downstream to create a resting pool
good riparian vegetation to shade resting pools and protect stream margins.
Learn more about how we can help Native fish in the city and how we can give our fish a hand! We also have two teacher resources with practical information for restoring streams for native fish – Planning for change and Planting stream edges.
Activity ideas
Saving taonga is an activity designed for students to learn about eels and/or whitebait and how human activity has impacted on their lives. Students learn about obstacles these taonga face and about possible solutions (mitigation) for the problems.
Investigate the effect of silage on rural streams with this unit plan.
In the Ake Ake – forever and ever activity, students learn about the Ake Ake model, a pictorial mapping model of individual perspectives that was developed and used with iwi on the Waikato River. Adapt this for students to explore changes in their local stream environment from a Māori perspective.
Acknowledgement
This resource has been adapted from the Hooked on native fish downloads developed by the NZ Landcare Trust. The Science Learning Hub acknowledges the help of the NZ Landcare Trust in adapting this work.
