The water level at Laguna de Bay declined slightly to 12.39 meters on Tuesday morning (Aug. 25), after reaching its critical high-water mark of 12.50 meters last week, the Laguna Lake Development Authority (LLDA) reported in an advisory.
The agency said the 12.39-meter reading was recorded at 10 a.m.
According to the LLDA, the lake reached its critical high-water level of 12.50 meters last week.’Since then, water levels have gradually receded following the cessation of intense rainfall associated with the recent tropical cyclone activity and the enhanced southwest monsoon,’ the agency said.
The LLDA considers 10.50 meters as the lake’s critical low-water level and 12.50 meters as its critical high-water level.
Despite the decline, the agency earlier warned of a continued high risk of algal blooms and possible fish kills in Laguna de Bay.
In its Aug. 21 advisory, the LLDA said prevailing cloudy conditions and the lake’s elevated water level were generally less favorable for immediate algal growth, which typically thrives in warm, sunny and stagnant conditions.
However, the agency warned that changes in weather and water conditions could trigger or intensify algal blooms.
The LLDA explained that warmer water can accelerate algal growth, while intermittent winds and rainfall can stir up nutrient-rich sediments from the lake bottom to the surface, providing additional nutrients that support algal proliferation.
Algal blooms can become harmful when the algae die and decompose, consuming dissolved oxygen in the water. Dissolved oxygen levels below 5 milligrams per liter can already stress fish, while further depletion may lead to fish kills.
‘This sequence of environmental events creates a direct mechanism leading to potential fish mortality,’ the LLDA said.
The agency urged aquaculture operators to closely monitor fish behavior, particularly during early morning hours when dissolved oxygen levels are naturally at their lowest.
Fish swimming near the surface or gasping for air may indicate low dissolved oxygen levels. When such signs are observed, operators are advised to immediately activate mechanical aerators or paddle wheels to improve water circulation and oxygenation.
The LLDA also recommended early harvesting if severe distress persists and the fish have already reached marketable size, to prevent mass mortality or fishkill episodes and minimize financial losses.
The agency also warned the public against buying or consuming fish found floating in Laguna de Bay, as decomposing fish may expose consumers to harmful bacteria.
Laguna de Bay serves as a natural catch basin for watersheds in Laguna and Rizal provinces and parts of Metro Manila. Rising lake levels therefore pose a potential flooding threat to low-lying lakeshore communities.