The recent fish kill that wiped out 80% of the fish cages in Lake Taal, Batangas with an estimated loss of P50 million was caused by a phenomenon known as lake overturn, according to specialists of the Los Baños-based Philippine Council for Aquatic and Marine Research and Development (PCAMRD) of the Department of Science and Technology.
A lake overturn takes place in deep inland water bodies like Lake Taal when the cooler mass of water at the surface is forced by winds to displace the warmer and oxygen-poor water mass at the bottom known as the hypolimnion.
In Lake Taal, overturns commonly occur in the months of December to February with the cool season and the strong winds of the Northeast Monsoon. Fish kills have also occured in the months of April and August.
Researchers of the University of the Philippines Los Baños and the Bureau of Fisheries and Aquatic Resources reported fish kills in the lake attributed to wind-induced overturns in 1993 and 2000. During such phenomenon, the surface water becomes acidic because of sulfur compounds brought up from the bottom and smells strongly of sulphur.
While lake overturns cannot be prevented the PCAMRD specialists say that fish cage farmers can prepare and minimize losses of their fish stocks by reducingn farming operations during the cool season and by not overfeeding and overstocking their fish in cages so as not to increase the organic load at the lake bottom. A continuous water quality monitoring and surveillance system is also recommended.