The music of rivers
Rethinking rivers mini series, Post 2 of 3: Rivers have their own distinct rhythms. Life evolves to match these rhythms — and when we disrupt them, ecosystems unravel.
It was World Water Week last week. It may have wrapped up, but the conversations it sparked are just beginning — and they matter more than ever. This is post two of a three-part series on some unique aspects of rivers and why they’re so challenging to manage. We’re exploring how rivers function as networks, their unique rhythms, and what that means for conservation and restoration. If you didn’t see it, here’s the first post:
Freshwater needs all the help it can get. By sharing these posts, you’re helping raise the visibility of ecosystems that are often overlooked — and increasingly at risk. Let’s get more people thinking about rivers not just as scenery, but as living systems worth protecting.
If I told you that you could make music from the flow of rivers, I’m sure you’d shrug it off and tell me I’m just being a nutter. But it’s true. And each river has its own music.
Before we get to the music, though, let’s talk about what makes these rhythms so wondrous, and why they matter for the life that depends on them.
One of the defining features rivers is that each has its own sequence of floods, droughts and all the bits in between — what we call the "flow regime". The natural flow regime concept was coined by colleague and friend LeRoy Poff back in 1997. It turned out to be one of the most influential papers in freshwater ecology. It defines the components of a river's flow regime into their magnitude, frequency, duration, timing, and rate of change.
These unique “signatures” of rivers are shaped by a whole suite of things like climate, geography, and geology. For instance, a river in the Colorado basin is characterised by long low-flow periods in winter because the precipitation all falls as snow and gets locked up in the hills until it is all released during spring floods. This is not the case in maritime climates like New Zealand, where rivers are at the mercy of storms rolling in from the roaring forties.
We can visualise these regimes graphically in what we call a hydrograph1. Think of it like sheet music for a river. It’s the record of notes that a river sings.
These rhythms aren’t just musical, they’re ecological — and evolutionary!
If a fish or riparian tree experiences the same rhythm for thousands of years, of course it's going to evolve to cope with or even capitalise on those rhythms. And that's just what happens.
Take the cottonwood tree that I've talked about previously. They've evolved to release their seeds in sync with the highly predictable snowmelt flood peaks that occur in systems like the Colorado. The Yampa River, above, is a prime example.
But many other adaptations exist: fish cue in on rising flows to begin their migration, insects evolve to synchronise their emergence to ensure they can meet each other and mate en masse, and amphipods time their egg laying with seasonal periods of low flood likelihood.
The types of adaptations, of course, depend on the predictability of the flow regime. Species living in the Colorado basin, for instance, have very different life histories to those from islands like New Zealand or Hawaii, where the climate is much less predictable, and so are river flows.
As I've talked about previously, species in unpredictable locations tend to be much more flexible and in fact often evolve strategies to hedge their bets. For example, mayflies in NZ that have multiple age groups of a population that live together compared to those in North America where all individuals of a single species emerge within a few hours of each other. In such numbers in fact that they block bridges and can be tracked on weather radars. This is a risky strategy if an unusual event hits.
Unfortunately, though, given the importance of these rhythms, rivers have been dammed and flows modified for centuries and continue to do so at an unprecedented rate.
One particularly pronounced way in which dams alter river rhythms is via hydropeaking. This is basically what happens when the whole town gets up, makes coffee, and nukes their porridge at once. In response, the dam releases water and generates electricity on demand. This creates daily cycles of flow that in some cases can be rather dramatic, like downstream of Hoover Dam.
When we drastically alter these rhythms in such an unnatural way, all manner of negative consequences emerge. For instance, as I've touched on in this deep dive before, hydropeaking in the Colorado River has led to the near complete loss of mayflies, stoneflies and caddisflies in sections of the river. The mechanisms behind this are complex so I'll save the full explanation for another day, but it relates to these unnatural tides that are created.
This is just one example of the impacts of altered flow regimes. There are many different forms. For instance, simply reducing or removing floods from a river can lead to the collapse of riparian ecosystems.
So, what does this all have to do with music?
Well, you know how I said a hydrograph is like the sheet music of a river? In this case it is. Friend and colleague from Colorado in the US, Dave Merritt, actually converted river flow regimes into music. How cool!
So, there you have it. You can actually make music from rivers. But their frequencies are more than musical — they’re ecological and evolutionary! So understanding these rhythms is essential for managing rivers in ways that supports biodiversity in all its forms.
Coming up in the next post
In the third part of this series, I'll talk about some of the challenges associated with conserving and restoring river species and ecosystems.
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Here’s 100 years of the Yampa River. Look how predictable that is — that beautiful rhythmicity!! Note, if you watch Dave’s video, he uses 1984 on the Yampa as one of his examples. See how it was an exceptionally high-flow year here. Click on the image to zoom in.
Fascinating! I love the mayfly hatching image—so cool!
What a beautiful rhythm to listen to of each river. Each it's very own song! And thanks for the info leading up to the video, it brings it all together. River/stream and springs flowing are so important to life!