This is an important positive message about fish passage.

We are seeing an increase in the use of the term “natural barrier”, particularly when prioritizing remediation of man-made structures/barriers.

As it happens, many species of fish have evolved to navigate what humans might think are impossible features.

There are now a number of effective fixes that are very low cost, thereby eliminating the need to prioritize in the first place.

All structures in waterways need to allow for fish passage regardless of what is above or below them.

Please watch and share this short video

This is a short video by Tim Olley showing larger bodied koaro (Galaxias brevipinnis) “climbing” up a natural feature.

Larger bodied fish tend to use a burst swimming action unlike the juveniles that typically “flip-flop” further out at the edges of the splash zone.

Smaller fish tend to be able to climb steeper slopes.

This rare footage shows both small and larger eels trying to navigate a natural feature. 
You will see that larger bodied specimens are unable to utilise the wet margins or splash zones. 
Remediation techniques should offer a range of options to give migrating fish choices to best suit their needs.

When designing new structures or considering remediation for existing ones, it is important to consider the swimming ability of the fish likely to pass through or over the structure.

This short video shows that small or juvenile fish operate at a very fine resolution not able to be easily measured or observed.

You will see in the video fish riding very subtle pressure waves within complex or nature-like flows that can have a different velocity and/or direction in the same location. 
It also shows fish climbing vertically when the conditions allow.