Fish-friendly streams provide diverse habitats for our native fish as well as supporting the insects and plants they need for food and shelter. Learn about the many different ways people can help their local stream environments, then jump in and give our native fish a hand!
Priority fish habitats for restoration include open streams such as those that travel through farmland, where the land has been cleared, with no riparian vegetation and small streams in catchment head waters in order to protect the source.
Sunny north and west-facing streams and streams where there is 200 metres or more of exposed water with no vegetation also need to be considered, as our native fish and the invertebrates they eat need shade and do not like water temperatures to get too high. Estuaries are also high-priority areas for protection and restoration as these are often spawning habitats for whitebait.
Before you develop an action plan and begin any work at a stream, you need to carefully assess and map it to find out what species live there and what issues are present for those species. There is evidence that some fish species are spawning in non-native grasses on riparian margins. By disturbing these, you may have a greater impact than you are aware. Check with NIWA or your local regional council before undertaking any restoration work.
You can learn about how to develop an action plan in Planning for change.
Clear the water
Sediment in streams clogs fish gills, makes it harder for them to find food and can also affect migration. Dense riparian vegetation helps to trap silt before it enters the water. For a short-term fix, you can secure hay bales across muddy ditches that enter your stream.
Livestock can also pollute water and stir up sediment. Keep them out by fencing off streams, and provide them with troughs or nose-pumps for drinking water. This also can help prevent the loss of stock that can become bogged down in muddy areas around streams.
Minimise drain maintenance
Farmland will often have large drains or waterways that are either naturally formed or dug specifically to drain excessive water. These are habitats for freshwater fish, invertebrates and other organisms. They are often interconnected and can also transfer water to other existing waterways. Excessive sediment, weed and algae growth can clog drains and cause flooding.
To minimise waterway disturbance, consider leaving some drains untouched and using registered sprays or weed rakes instead of digger buckets to remove excess weed growth. Regular disturbance using diggers can damage habitat and disturb feeding and spawning of fish. It can also dislodge sediment, which can cause problems downstream. Ensuring any disturbance to the drains is carried out in late summer/early autumn will avoid upsetting fish that are in the spawning and migration phases of their life cycle. This gives them a greater chance of survival.
Objects in waterways like logs and boulders can cause headaches for flood managers and create hazards for swimmers and boaties, but fish need in-stream debris. This debris provides fish with:
- a shelter from strong currents
- a place to escape predators
- shade and cover during the day
- somewhere to lay their eggs – on or under the debris depending on the species
- a place to trap food.
It also supports biodiversity by trapping leaves and detritus, providing a habitat for various insects (that will in turn provide food for fish).
When encountering debris, assess it first. If it is stable, leave it in the stream, and think twice before removing large trees that fall into waterways if they pose no hazard.
Encourage fish passage
There are a number of strategies you can use to assure fish can migrate to and from the stream – the strategies and methods you use will depend on your initial assessment and action plan.
If the stream flow is rapid, creating a rough bed will help to slow the water flow. You can also create resting areas for the fish, such as leaving stable debris in the stream or creating baffles. A baffle is a rocky substrate or a brick or something similar that gives the fish something to climb up on to rest.
If there are existing culverts that are impeding fish, you can retrospectively fit ramps or fish ladders and baffles.
If new culverts need to be installed, make sure they are fish-friendly. A fish-friendly culvert will have slow water flow (most of the time), rest areas for the fish and a water depth of at least 10 centimetres and will be level with the stream or have structures that don’t require the fish to jump.
The culverts should also fit with the environment and mimic the natural streambed by following the natural slope and original streambed direction. Ideally, they’ll be wider than the stream at average flow and large enough so that they are never more than half full of water when water flow and levels are at their highest in the stream. Again, this work should be carried at a time that will not affect the spawning and migration habits of the species in your stream.
Fixing your stream edges
Planting and fencing stream edges can significantly improve water quality and fish habitats.
Our native fish thrive living in clean streams and rivers lined with native grasses, trees and shrubs. Many native freshwater fish require habitats with bushy overhangs that shade the water and provide cover for them to escape predators and keep water temperatures low to ensure their invertebrate food source is in abundance. Fish, such as some whitebait species, lay their eggs on long grass, sedges and rushes by coastal streams and estuaries.
The vegetation on the stream edges also helps to stabilise the banks and reduce sediment run-off into the water. Densely planted sedges, native toetoe and flax also help trap nutrients, bacteria and other pollutants before they enter streams and waterways.
Furthermore, the plants drop leaves and insects into the water for the fish to eat!
Getting rid of weeds is also important. You will want to identify pest plants that might be choking out the native plants that play an important role in the stream ecosystem.
See the teacher resource Planting stream edges.
Finally, don’t forget about pest control! Rabbits, hares and possums can destroy vegetation – especially new plantings. There are many methods of predator control currently used in New Zealand. Local regional councils are often able to help with information or by supplying traps. Predator Free NZ also offers a number of useful resources.
Learn more about these methods and consider some of the pros and cons in Methods of predator control.
Other pests are those that predate on our native fish. Pest fish such as koi carp and Gambusia (mosquitofish) prey on native fish and insects. Gambusia are particularly aggressive, frequently attacking native fish, nipping at their eyes and fins. Our endangered galaxiids and mudfish are especially vulnerable. These pests also compete with native fish for food and have been known to eat native fish eggs.
Though it’s best to leave pest fish eradication to the experts, you can help minimise their spread by carefully cleaning boating and fishing gear between waterways to destroy eggs. Never release pest fish into the wild – it’s illegal!
Learn more about some of the research and work in the Waikato to eradicate koi carp in Trapping koi carp.
Predator Free 2050 vision – pest predators have a significant impact on vegetation around our streams and also on our native wildlife.
Many of the strategies to help our native fish thrive are about restoring habitats and biodiversity. Examples of activities to promote student thinking about biodiversity and habitat loss are Threats to biodiversity and Biodiversity battleships.
In the activity Hubbub Estuary, students are encouraged to identify some possible impacts on estuaries and possible actions that can be taken to protect them. This could be adapted specifically for a stream environment or used as is for those who are looking at a stream that runs into a local estuary.