The significant reduction of algal biomass production in Laguna de Bay, along with the practical disappearance of zooplankton, is choking the fish species endemic to the lake.

These facts have been known to the Philippine government for the last five years but little, if ever, was done to arrest these disturbing developments.

The Millennium Ecosystem Assessment (MA) conducted in 2005 showed that the massive algal blooms of the 1980s have not materialized in recent years, an indication that there is not enough oxygen to nourish them.

Moreover, the assessment revealed, “Laguna de Bay is presently perennially and critically turbid. Its secchi disk transparency ranges from 0.1 m to 0.8 m with an average of 0.4 m. This physical deterioration of the lake dates back to the 1980s or earlier, when big infrastructure projects were being constructed and operated at the same time that a fishpen sprawl was underway. The present depth of light penetration indicates that the lake is dystrophic, meaning it is critically turbid. In its downgraded physical state, the lake has become less hospitable to the photosynthesizing algae that are a natural food to aquatic animals. This type of a relationship may translate into a deteriorated quality of the natural food for fish.”

At the same time, the lake is getting shallower in spite of reports that the latest recorded average depth is 2.7 m, which is deeper than the earlier reported average depth of 2.5 m.

“The higher average stems from the narrowed range of its depth. Rapid shoaling is due to the high rate of organic and inorganic matter deposition. Organic deposition is high where the aquatic macrophytes proliferate. Inorganic deposition is accounted for by the tributary rivers and streams,” the report said.

Even the zooplankton colonies in the lake have been affected, with less and less of such colonies materializing as the fishpen area gets bigger.

“Reduction of the latter seems to have made way for the zooplankton populations to grow. The zooplankton community dynamics in the lake need further elucidation,” it noted.

The researchers also complained that the normal clearing of the lake when saltwater intrusion from the Pasig River happens does not appear to be occurring.

“It is to be expected that Laguna de Bay is accumulating salts from the normally occurring, periodic exchange of waters with Manila Bay. The lake has been seen to exceed the recommended safe level for Class C water resources (350 mg l-1) most especially in summer, in various places. Regardless of the increased salinity, Laguna de Bay remains highly turbid today. This means that the expected flocculating effect of saline water when this meets freshwater is no longer markedly evident in the lake because of a strong turbidity development due to sediment re-suspension in this shallow lake,” the report said.

What has caused more concern for the analysts was the fact that the water of the lake is “contaminated with toxic and hazardous substances (e.g., heavy metals and persistent organic pollutants including pesticides) coming from the industrial and agricultural sectors. The heavy metals Pb, Cr, Cd, Cu, As, and Hg, at one time or another, have been found in concentrations exceeding the prescribed safe levels for Class C waters.”