1. Cause and effect

Algal bloom is a periodic occurrence in Laguna de Bay, particularly in the Central Bay and West Bay, where Muntinlupa City is one of the lakeshore LGU’s.Aigae are microscopic plants in various forms, shapes and colors. Those commonly found in Laguna de Bay are blue-green algae, green algae and diatoms. They are natural food and their abundance in lake is one of the factors attributed to the success of aquaculture business in the lake. Aside from being a source of food for fish and other aquatic life, these algae provides dissolved oxygen through the process of photosynthesis.

The over supply of nutrients in Laguna de Bay like nitrate and phosphate makes the lake very eutrophic, or in layman’s term , very fertile. Combined with environmental conditions such as sufficient sunlight, high water temperature and calm water, the algae can grow at a very fast rate. If these environmental conditions aresustained, algal bloom happens which appears like a thick green or blue green soup. The current algal bloom in the West Bay area of the lake is caused by Microcystis, a blue­ green algae which has been classified as a cyanobacteria.

Algal bloom becomes harmful when they decompose. In the process, they use the dissolved oxygen in water. Oxygen level below 5 mg/L is already stressful to the fish and if it further decreases, fish kill can occur. Should this happen, it is strongly advised to harvest the dead fish and bury them in the soil. Leaving them rotting in water will further aggravate the situation.

Microcystis also contains chemical compounds, like geosmin and 2-mib (methyl-isoborneol ), which are released in water when their cells break. These compounds cause odor and taste problems in fish and also emit earthy smell. Exposure to algal bloom can cause headache and nausea.

2. Can we prevent algal bloom? How?

Yes, we can prevent algal bloom. We cannot control the weather, but we can control the amount of nutrients entering the lake. They originate mostly from untreated domestic wastes, agricultural wastes and industrial wastes. However, infrastructure and financial support are needed to treat these wastes, thus it will take a longer time to put them in place.

A doable measure is to ensure that our septic tanks are working well and regularly de-sludged. Proper sanitation by communities along the riverbanks and the lakeshore needs to be practiced. Dumping of organic wastes in waterways must be prevented and regular cleaning of drainage canals, creeks, esteros and rivers must be practiced as required by the DlLG and the DENR.

The LLDA shall allocate PHP 1M for clean up activities by its Environmental Army in coordination with the Local Government of Muntinlupa City. It will explore means to purchase an algae skimmer that can be deployed in affected areas. It will further step up its efforts to inspect all business establishments in the watershed to ensure compliance to effluent standards, and enhance its partnership with local officials to improve environmental compliance of communities to various environmental laws.

Related News: Muntinlupa City gets P1M for Laguna lake cleanup – Inquirer.net