Unprecedented Fish Die-Off Draws Attention to Water Quality in Vietnam’s West Lake

This past weekend, a major fish die-off occurred in West Lake, the largest freshwater lake located in Vietnam’s capital of Hanoi.

Although smaller fish die-offs are common, this event is reportedly to be of unprecedented seriousness. The large number of dead fish floating in the lake and resulting overpowering smell caused local authorities to call in the People’s Army to haul the dead fish out of the lake.

While authorities have not yet announced the cause of the fish kill, the uncontrolled release of sewage and waste into the lake have given rise to high levels of nutrients. The water is commonly a dark green color, but it was reported that a different green color was seen on the surface of the lake on October 1.

It is likely that a decrease in water temperature reached the optimal growth rate of the algae. This caused an algal bloom with the algal respiration at night consuming the dissolved oxygen in the lake and creating a state of acute ecological hypoxia, ultimately leading to the death of a large number of fish in the lake.

Hopefully this is a wakeup call to the authorities to stem the flow of untreated waste into the lake, some estimates of which are 4,000 cubic meters per day.