Brackishwater aquaculture production in Lingayen Gulf in northwestern Luzon, Philippines, is one of the highest in the country. Most of the aquafarms are mangrove forest and marginal lands which have been converted for milkfish and shrimp culture. Brackishwater aquaculture development has been closely associated with mangrove forest denudation. In recent years, the ecological importance of mangrove forests has been recognized, especially as nursing and feeding grounds for many aquatic species. This has led to efforts in mangrove reforestation and conservation. Are there potential sites for brackishwater aquaculture expansion in the Lingayen Gulf? A site selection study using geographic information systems (GIS) identified about 16,000 ha of potential sites that excluded major agricultural land uses and mangrove reforestation areas. For mangrove reforestation, about 12,000 ha have been identified. The results of this study are as yet preliminary and further work is needed to determine the actual potential sites.