Dr Hiranya Sudasinghe: Could Tidying a Stream Be the Worst Thing You Do to It?

STORY 4 OF 10: Part of a series of short stories inspired by our conversation with Dr Hiranya Sudasinghe, sharing what years of experience have taught them to see.

The streambank looks untidy.

Roots twist into the water. Leaves gather against fallen branches. Plants lean over the bank with no apparent respect for property maintenance.

Someone arrives with a blade and an entirely reasonable intention:

Clean the place up.

The fish would prefer that they did not.

Vegetation provides shade. Roots hold the bank together. Leaves and insects enter the food web. Fallen wood creates shelter and changes the movement of water.

What looks untidy to a person may be working extremely well for a fish.

Intact stream bank with overhanging natural canopy, tree roots and leaf litter. Photograph courtesy of Hiranya Sudasinghe.

When Hiranya was asked what someone living beside an intact rainforest stream could do, he offered an unexpectedly modest answer:

Not very much.

Where the stream and its surrounding vegetation remain intact, unnecessary intervention may cause more harm than benefit.

Where banks have already been cleared, restoration can help.

But “locally appropriate vegetation” matters.

The same convenient tree should not be planted beside every stream simply because it is fashionable in restoration projects.

The plants should reflect the natural vegetation, rainfall, soil and conditions of that particular place.

And a shaded bank cannot protect a fish if a house, farm or business sends untreated wastewater into the stream.

Hiranya’s words that inspired this story

“Something that you can easily do is not do much.”

“To maintain a fish, for a stream, the important thing is to maintain the bank.”

“The idea would be as natural as it could be.”

“You have to have a better sewage plan and everything to make sure you’re not polluting those aquatic systems.”

Why it matters

Clearing streamside vegetation can

• Warm the water

• Destabilise the banks

• Increase erosion

• Add sediment

• Remove shelter

• Reduce food entering the stream

• Break the natural corridor along the bank

  
  

The tree beside the water is not scenery around the fish habitat.

It is part of the fish habitat.

What this changes

Where a stream remains natural,

Leave it as intact as possible.

Where the bank has already been cleared,

Restore vegetation suited to the place.

Where wastewater enters the stream,

Redirect and manage it properly.

The action is refreshingly free of heroics.

Sometimes conservation begins by putting down the clearing tool and redirecting the drain.

Next beneath the surface

Another well-intentioned action begins when an aquarium fish becomes too large and releasing it feels like the kindest option.

Next: Can Saving One Aquarium Fish Harm Thousands of Wild Animals?

Previous: Why Can’t a Protected Forest Protect the Stream Running Through It?

Meet Dr Hiranya: Read He Chose the Fish