Sungai Mansahaban - the river that passes through Marakau village in Ranau, Sabah - is translucent and always flowing, uninterrupted.

If you descend into the river with a fistful of fish food, a swarm of carp (koi) and some ikan pelian - the native Malaysian Mahseer fish, also known as ikan kelah - rushes like a magnet towards you.

The river was not always this clean and bountiful.

Resident Hamdan Jaini said it used to be dark, murky, and choked with trash. As for the fishes? There were none.

With Tagal, “we returned the river to what it was,” an emotional Hamdan said, holding back tears as the river gushed into a...