Sustainable fisheries development partly depends on the availability of adequate zooplankton as principal food items of early life history stages of economically important fish species as well as of the adults of some species such as clupeids (e.g., Sardinella tawilis of Lake Taal in Batangas). The broad characteristics of the composition of freshwater zooplankton (Rotifera, Cladocera and Copepoda) of natural and man-made lakes in the Philippines are compared with those of the Oriental Region, in particular, and other tropical regions, in general. Two species of calanoid copepods are endemic, a somewhat remarkable occurrence considering that calanoids are represented by only five known species in the Philippines and absent in many large tropical lakes. Daphnia, which almost invariably influences food-web interactions and structures of plankton communities in temperate lakes, still has to be recorded.

Geographically located in Central Mindanao, Lake Lanao is the second largest lake in the Philippines. The lake is famous locally for its various uses and internationally for its endemic cyprinids. This paper intends to inform the local leaders and the national planners about Lake Lanao's dwindling fisheries resources, the extinction of some endemic cyprinids, and the current interventions as well as suggested action plans to increase fish production and to conserve the remaining species in the lake. The past and present studies on the lake are also reviewed. Early and latest statistics on the lake's fisheries production are presented to invite the interest of all sectors in coming up with the integrated approach to protect, conserve and increase its fisheries production. Local and national interventions to conserve and increase fisheries production are discussed. These include the setting up of BFAR Fisheries Station in Kialdan, Marantao; the establishment of a fish hatchery in Poona, Marantao by Southern Philippines Development Authority; the formation of Save Lake Lanao Movement by the local leaders; the creation of Lake Lanao Research and Development Council; the current concern of Philippine Council for Aquatic and Marine Research and Development-DOST; and the extension and research and development thrusts of the Mindanao State University, College of Fisheries in Marawi City.

A lake model originally developed for Shin-Nippon Meteorological and Oceanographical Consultants Co., Ltd (METOCEAN) was used with modification to simulate the water quality of Laguna de Bay. The METOCEAN model made use of the 1984 meteorological and water quality data collected from different local government agencies. Hydraulic modeling was applied to obtain basic circulation patterns which the water quality modeling was based upon. Results of the hydraulic modeling suggests that steady backflow of saltwater from Pasig River reaches deep inside the bottom layer of the lake although the lake water flows out through the Pasig River. Thus, the water quality model for Laguna de Bay focused on the unique role of the salt water intrusion in limiting phytoplankton productivity. The effect of saltwater intrusion was simplified as the change of depth of euphotic zone in the lake water estimated from the Secchi disc transparency. For simplicity and expandability of the model as a predicting tool, Secchi disc transparency was the only forcing function considered in the study. Modelling resolution of water quality has 4 boxes horizontally and 3 levels vertically. Calibration of the water quality model was carried out by running the model repeatedly until satisfactory agreement with measured data was obtained under average wind condition (Eastern wind, 1.5 m/sec.) Other wind directions including no wind condition were also tested to see the effect of wind on water quality. Validation of the water quality model was done for 1985 to 1988 as continuing simulation from the calibration in 1984 under the average wind condition. Then simulation of the condition of the lake from 1991 to 1995 based on the 1984 data used in the calibration was tried changing only the Secchi disc transparency data. Initial results of the water quality model differentiated conditions with and without saltwater intrusion. Without saltwater backflow, higher concentration of total inorganic nitrogen and inorganic phosphorus and low dissolved oxygen especially in the bottom layer are predicted. Under this condition, release of large amounts of nutrients in the sediments is expected to be dominant source of total inorganic nitrogen in the lake. The study is the first attempt to model the lake. The model still needs calibration and validation with measured values of recent years before adapting its usefulness as a tool for predicting water quality of Laguna de Bay.