Lake Mainit, the Philippines’ fourth largest and deepest lake, is a significant freshwater body located in the northeastern region of Mindanao. Spanning 173.4 square kilometers and reaching a maximum depth of 223 meters, this oligotrophic lake is shared by the provinces of Surigao del Norte and Agusan del Norte. It plays a vital role in supporting biodiversity, local livelihoods, and the cultural heritage of surrounding communities.

The lake is bordered by the municipalities of Mainit and Alegria in Surigao del Norte, and Kitcharao and Jabonga in Agusan del Norte. These lakeshore towns, along with other municipalities within the watershed, such as Sison, Tubod, Santiago, and Tubay, constitute a network of communities whose livelihoods are closely linked to the lake’s resources.

The name “mainit” derived from the Visayan word for “hot,” reflects the presence of geothermal springs in the area. Beyond its name, Lake Mainit serves as an important ecological habitat and a vital resource supporting the well-being of thousands of residents.

Fishery resources and cultural significance

The fisheries sector plays a central role in the ecological and economic importance of Lake Mainit. A study conducted by Southeast Asian Fisheries Development Center (SEAFDEC) in 2007–2008, documented the presence of at least 15 species of aquatic plants, five species of crustaceans, 10 mollusk species, and 41 fish species in the lake. Among these is the native white goby (Glossogobius giuris), locally known as pijanga, which is considered one of the most important fishery resources. Other economically significant species include mudfish (Channa striata), tilapia, carp, and eel, many of which are staples in local diets and are closely tied to cultural practices.

Fishing serves as a primary source of livelihood for over 4,000 individuals residing around Lake Mainit, many of whom employ traditional and artisanal fishing methods. A 2015 socio-economic study by Mindanao State University (MSU) underscored the critical yet often overlooked role of women in the fisheries value chain, particularly in postharvest processing and fish vending, where they make substantial contributions to household incomes and local food security.

Economic importance, environmental concerns

Lake Mainit contributes to the Philippine economy through various means, including freshwater fisheries, agricultural irrigation, and potential eco-tourism and community-based enterprises. A study conducted by Caraga State University estimated the lake’s total fishery income at over Php 724 million in 2015, highlighting its significance in regional food systems and rural livelihoods.

Despite its economic value, Lake Mainit faces increasing environmental challenges. Overfishing, pollution, and habitat degradation have contributed to a 63 percent decline in fish catch by the year 2000, compared to levels recorded in the late 1990s. Key species including pijanga (white goby) and kasili (eel) are now caught in reduced sizes and quantities. Additional pressures on the lake include sedimentation, the spread of invasive species, and weak enforcement of fisheries regulations.

Promoting stewardship and sustainable management

In the face of growing environmental challenges, efforts to safeguard Lake Mainit continue. Since 1999, the Lake Mainit Development Alliance (LMDA), a consortium of local government

units, has worked to integrate fisheries management into broader conservation and development frameworks. Initiatives include community education, the promotion of sustainable fishing practices, and policy reforms are gradually being implemented at the local level.

In support of science-based management, the DA-NFRDI, in collaboration with

the DA-Bureau of Fisheries and Aquatic Resources (BFAR), conducts regular assessments of the lake’s fish stocks through the National Stock Assessment Program (NSAP).

To further protect the lake’s biodiversity, DA-NFRDI and its partner stakeholders have also evaluated the presence and potential impact of non-native fish species in and around the lake. These activities aim to provide a sound scientific foundation for more effective and adaptive fisheries management strategies.

Lake Mainit is not only a valuable ecological resource but also a vital component of local cultural heritage and economic stability. Its conservation is both an environmental responsibility and a socioeconomic priority. The long-term sustainability of the lake depends on the continued commitment of all stakeholders who rely on its resources. ### (Norvida Gatdula)