Fish kills that occurred in certain areas of Rizal province in June may have been due to the rapid increase of algae in Laguna Lake, according to the Laguna Lake Development Authority (LLDA).
LLDA personnel conducted an investigation of the reported fish kill in various parts of Laguna Lake, particularly in barangays Malaya and Quisao in Pililla, Rizal, and in barangays Kinaboogan, Kaytome, Clarity, Limbon-limbon, and Ithan in Binangonan, Rizal.
Earlier reports said that “hundreds” of fish such as tilapia and carp were lost due to the fish kill last month.
Based on the LLDA’s investigation, there may have been an increase in the number of “liya” or freshwater green algae in these areas caused by extreme heat. But when it rained, the water temperature in the lake possibly drastically changed that led to the death of the “liya.”
LLDA further explained that oxygen in the water has been depleted due to the decaying “liya” which caused the fish to die from their cages.
“Ang pagdami ng liya sa lawa ay nakakatulong sa mabilis na paglaki ng isda ngunit sa panahon na ito ay sobra ang dami ay maaaring magdulot ng masamang epekto sa mga isdang nasa fish cages o fishpens. (The increase in the number of liya in the lake contributes to the rapid growth of the fish but during this time too much liya caused adverse effects to the fish in cages or fishpens),” it said in a Facebook post last June 22.
The algal bloom may have been caused by the Microcystis aeruginosa that usually increases in number when the lake is calm, the weather is very hot, and there are many nutrients in the water that are mainly coming from households around the lake, the LLDA said.
It added that the increase in “liya” is noticeable when the water in the lake becomes green and as they increase they form a dense layer on the surface of the lake.
“May pagkakataon na ang lawa ay mistulang may pinturang kulay berde na nakalutang. (There is a chance that the lake would look like it has a floating green paint),” it pointed out.
LLDA advised fish cage or fishpen operators that if they notice that the fish are swimming and gasping for air on the surface of the water, it is recommended to run their motorboat in an area where there is less oxygen to compensate for the lack of oxygen in the water and to prevent the formation of “liya.”
They can also use gasoline aerators or paddle wheels to address oxygen deficiencies, it said.
These should be done every two hours at night until dawn, it added.