The consequences of this unfolding tragedy are many, with its swirling currents flowing from global markets to transnational organised crime networks preying on the poverty of young men who scrounge for gold. One upshot is critical water systems fouled by a toxic combination of sediment and chemicals.

The consequences of this unfolding tragedy are many, with its swirling currents flowing from global markets to transnational organised crime networks preying on the poverty of young men who scrounge for gold. One upshot is critical water systems fouled by a toxic combination of sediment and chemicals.

Last year, Dr Francois Roux detected something unsettling in the Blyde River. An aquatic scientist with the Mpumalanga Tourism and Parks Association (MTPA), Roux has been studying Lowveld large-scale and Bushveld small-scale yellowfish for more than 20 years.

But last year, for the first time, Roux found that both species had failed to spawn -- an ecological shock linked to a surge of illegal gold mining in the area as zama zamas and their bosses scramble to cash in on record prices.

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"It's a monstrous thing, and it happened where we thought it would never happen," said Roux.

Sediment stirred up by an estimated 2,000 zama zamas has smothered the eggs of the yellowfish, which have become aquatic versions of the canary in a coal mine, their fate a stark warning of what may befall ecosystems downstream, including in the Kruger National Park, and the water that supplies towns and provides irrigation for...