Dr Hiranya Sudasinghe: Why Can’t a Protected Forest Protect the Stream Running Through It?

STORY 3 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.

A forest reserve has a boundary.

A stream has other plans.

It may begin inside a protected forest, pass through a plantation, run beside homes, cross a road and receive several drains before continuing downstream.

The fish experience all of it.

Much of Sri Lanka’s endemic freshwater-fish diversity is concentrated in the southwestern wet zone, broadly between the Attanagalu Oya and Nilwala river basins.

A wet zone stream running through a mixed-used human landscape. Photograph courtesy of Hiranya Sudasinghe.

This is not a distant wilderness separated from human life.

It is a landscape of homes, farms, plantations, roads, towns and businesses.

Many rare fishes therefore live not beyond society, but inside the parts of the country where society is most active.

A disturbance upstream does not remain politely at its point of origin.

Remove vegetation, and soil may wash into the stream.

Direct polluted drainage into the water, and it travels downstream.

Alter the flow in one location, and habitat changes elsewhere.

A stream must therefore be understood as part of a catchment, the wider area from which water drains into it.

A stream can also still look like continuous habitat while sections of it have become barriers that fish cannot safely cross.

A dam, culvert, polluted section, modified channel or stretch of unsuitable water can divide one fish population from another.

The fish may still have water around them, but no safe route to neighbouring populations.

A stream can therefore be damaged in two ways.

Its habitat can become poorer.

Or its remaining good habitat can become disconnected.

Hiranya’s words that inspired this story

“Our endemic diversity is mostly in the southwest wet zone.”

“Most of those freshwater habitats are outside of protected areas.”

“If there’s disturbance upstream, there can be lots of sediment accumulating downstream.”

“Habitat fragmentation, habitat degradation in a broader sense, and then these exotic species face a very big threat.”

Why it matters

Protecting one section may be inadequate when

• Pollution enters upstream

• Streambanks are cleared elsewhere

• Dams or culverts block movement

• Sediment travels downstream

• Water is extracted before reaching the protected section

• Good habitats become isolated from one another

  
  

A boundary can control people.

It cannot persuade water to stop flowing.

What this changes

Freshwater conservation belongs not only to protected-area managers.

It also belongs to local authorities, farms, businesses, housing developments, road designers, landowners and households.

A stream connects decisions made by people who may never meet one another.

Next beneath the surface

One of the most damaging decisions may begin with an entirely reasonable desire to make the stream look tidier.

Next: Could Tidying a Stream Be the Worst Thing You Do to It?

Previous: Can Two Identical-Looking Fish Carry Different Histories?

Meet Dr Hiranya: Read He Chose the Fish