Last Sunday morning, Bryan Ang woke up onboard his floating fish farm on the Johor Strait between Malaysia and Singapore to find nearly all his stock had died.

 

He was not alone. Hundreds of tonnes of fish - both farmed and wild - died over the weekend in the eastern part of the strait. Fish farmers lost hundreds of thousands of dollars in stock overnight.

 

Floating out at sea and washing up on the beaches and mangroves, dead sea creatures began to appear, from sea snakes and seahorses to squid and moray eel.

 

Nature guide and environmental biology student Sean Yap - who supplied some of these pictures to the BBC - said he was jogging along the eastern Pasir Ris beach on Saturday evening when he smelt a foul stench.

 

It came from what he described as a "mass grave" - thousands of dead fish washed up on shore.

 

The environmental authorities said the deaths were due to a plankton bloom, where a species of plankton multiplies rapidly, damaging the gills of fish. It can be triggered by sudden changes in temperature, high nutrient levels in the water, and poor water circulation.

 

Government agencies were unable to provide the BBC with figures, but said they were "concerned" about the potential impact on marine biodiversity and were taking steps to investigate and help farmers clean up.

 

There have been similar mass fish deaths in the past five years. This time round, the authorities had given an early warning to farmers - giving them time to move their stock into protective nets, activate pumps to keep the water moving or even float their entire farm to safer areas.