Go The West Coast!

Happy to share that the West Coast (South Island NZ) has embarked on a fish passage remediation program beginning with road culverts.

Tim Olley and Richard Nichol spent a couple of days near Reefton improving fish passage through culverts on the access road to the Paparoa Track – Great Walk. 

They completed several fixes using various methods such as flexible baffles, mussel-rope, floating ramps and rubber strips.

Keep up the great work!

Tim Olley,
Floating ramp. Flexi-baffles throughout
Richard Nichol,
Rubber ramp with mussel-rope. Flexi-baffles throughout

Mussel-Rope Heads-Up

Many of you will be familiar with the use of mussel-rope to help improve fish passage over or through structures including culverts.

The rope helps to reduce the water velocity adjacent to the rope and also gives a tactile surface for small fish to wriggle through or over.

Rope is a good tool when there is no other option, however it does not create resting pools, add depth, or retain bed-material.

While we have installed many 1000’s of meters of mussel-rope, it is important to understand that there are limitations as to where mussel-rope can be used and where it is not suitable

Mussel ropes can be used to enhance fish passage on existing structures where: –

  • Culverts are perched and fitting ramps is not practical.
  • It is not practical to install baffles e.g. culvert diameters <800mm

Other notes:

  1. Based on our extensive experience, it is best not to attach the downstream end of the rope as this has been known to cause blockages when logs, debris etc gets caught under the rope.
  2. Fixings should be roust e.g. stainless steel D-ring and clasp – NOT a waratah.
  3. “Swimming lanes” are rarely achievable when installing ropes through smaller diameter pipes because these pipes typically have very low flow. It is even more challenging if the pipe is also long.
  4. There is no evidence that “swimming lanes” are more effective than a number of ropes laying close beside each other.
  5. When aiming to get fish up a perched or overhanging structure, it is best to first attach a strip of rubber in order to create a wetted margin.                                    See Tim’s video link below.
  6. Looped-rope is less likely to shed fibers than Super-Christmas-tree rope and there is no evidence of it being more likely to cause a blockage.
  7. The cut ends of the ropes should be melted to prevent fraying.
  8. If rope is used through a culver that is also overhanging, there should be twos sets – one set attached at the upstream end and finishing at the outlet, with a second set attached at the outlet hanging down into the plunge-pool.

In summary:

Mussel-ropes should only be used as a last resort when remediating existingstructures where ramps, baffles etc are not practical.

We are always willing to listen, help. share and learn, so please feel free to contact us however and whenever..


This short video shows elvers climbing across both smooth and rough surfaces. 

The urge to overcome obstacles is powerful and you can see individuals climbing over each other.

The more we watch these creatures, the better we understand their capabilities and limitations when we are considering remediation.

Click here or on the image below

Nelson City Fish Passage Restoration Program

Here in NZ it was Conservation Week last week.

Barriers to Fish Passage, is certainly making the headlines, particularly with the announcement of the National Policy Statement Freshwater Management (NPS-FM 2020).

Nelson City, NZ has been ahead of the game, with a region-wide program well underway, remediating a range of structures with effective, robust, and low-cost fixes.

The city council has posted this excellent short video highlighting some of the work completed so far.

Conservation Week – Helping our native fish swim against the current

It’s #ConservationWeek and here’s today’s conservation video. This video shows how concrete pipes and culverts make it hard for native fish to swim up and down our streams so we have to put in deflectors to slow the current down and make places for them to rest. That helps them swim upstream to spawn and keep their populations healthy. Comment on this video and you will go into the draw to win a family pass to The Brook Sanctuary.

Posted by Nelson City Council on Thursday, 20 August 2020

 The NCC fish passage program is very simple  – see below:

1. Locate structures in the waterway
2. Survey of structures in waterways and give a “Current Status”
3. Identify barriers to fish
4. Consider desired and undesired fish species
5. Propose mitigation and costs
6. Propose some form of prioritisation for remedial works
7. Undertake remedial works
8. Reporting and data management
9. Ongoing monitoring

Another YouTube version of the video below.

Field Day

I had a great day out in the field with a bunch of folk keen to do some learning with gumboots on.

Kelsey Tills of Rayonier kindly organised the day with representatives from Forestry (Rayonier and PF Olsen), local government (Waikato Regional Council), contactors and a community care group.

Despite the rain, we manged to visit a number of culverts and discussed both new installations and remediation of existing structures, with a view to improving fish passage.

The Fish Passage Action Team are happy to assist and or lead workshops or training days.

Fish Passage Workshop – Whangamata,NZ.
Photo – Glenda Betts

Note: This culvert is under a road that crosses a wetland – there is no stream as such, just what was excavated during the installation.

Focus On Maintaining Fish Passage During Low Flows

It is worth remembering that lows flows and shallow water are challenges to migrating fish. 
The video below represents remediation to an upgraded urban storm water pipe serving a small tributary of the Maitai River near Nelson, NZ.

The upgrade involved upsizing the pipe and removing the perch at the outlet.

– Base flows of the tributary are approximately 1L/S
– Pipe length 300M
– Pipe gradients range from 2%-12%

You will see an increase in the depth and width of the water along with bed-material beginning to accumulate.

Climbing Redfin

Tim Olley captured this rare footage of a juvenile redfin bully (Gobiomorphus huttoni) climbing up a retro-fitted mussel-rope with backing, into an overhanging culvert.

It reminds us that, given half a chance, many fish will navigate challenging obstacles.

What is not well understood, is what precise factors cause a fish to transition from a swimming to a climbing mode of locomotion.

Reservoir Video

Below is one of Tim’s videos featuring the culvert remediation project in the recently published “Lessons Learnt 8”.

There is some great underwater footage showing how fish navigate upstream utilizing the back-eddies and rest pools created by the flexible baffles.

For those that missed the write-up check it out here

GIS Project

Jordie McDonald has completed a desktop GIS project highlighting the huge number of potential barriers to fish passage in the Northland Region of New Zealand.

The extent of the potential barriers is probably typical around NZ the rest of the world.


We will soon share a report on a large catchment where each site is visited and assessed. A “current status” is assigned to each in order to give a better picture of what is out there and what needs to be done to remediate. Enjoy!