Environmental problems have significantly affected fishery production and management in Laguna de Bay, the largest lake in the Philippines. Fishermen and fishpen operators are complaining about the slow growth of fish and low yields in the lake. In the 70’s two croppings were possible in fishpens since it took only 3 to 4 months then rear milkfish from fingerlings to marketable size (Felix, 1976). But in the early 80’s, stocked fingerlings attained a marketable size of about 200 g after 8 to 15 months (LLDA, 1983). In 1973 when the total fishpen area was only 5,000 ha, the annual harvest was 4 metric tons (MT)/ha. When fishpens covered 31,000 ha of the lake area in 1982, the annual yield dropped to 2 MT/ha (Centeno et al., 1987). Furthermore, the total open water catch of nearly 83,000 MT in the early 60’s (Rabanal et al., 1964) was reduced to one-fourth in the 80's. While the big drop in yield has been largely attributed to the proliferation and mismanagement of fishpens, over-exploitation of lake resources, and seasonal changes in the productivity of the lake (Centeno et al., 1987), the author attributes the present crisis basically to a lack of understanding o the basic ecological attributes of Laguna de Bay and their relation to fish growth and production. This paper is a brief commentary on the Limnological characteristics of Laguna de Bay tat are quite important in finfish production.