Wadaslintang Reservoir is located in Wadaslintang, Wonosobo Regency, Central Java, Indonesia. Positioned in southern Wadaslintang, it borders Padureso District in Kebumen Regency. The reservoir is approximately 46 kilometers from Wonosobo and collects water from the Medono River and several tributaries, including the Lancar, Waturangkang, Somagede, and Tritis rivers. As of 2006, this 1,320-hectare reservoir was recognized as having one of the tallest dams with a global wet core.
Wadaslintang Reservoir has long been a crucial water resource for the surrounding communities, supporting various needs such as fisheries, floating net cages (FNC), tourism, and supplying clean water for irrigation and consumption. Additionally, it serves as a renewable energy source through its hydroelectric power plant (PLTA), which contributes to the local power supply. The reservoir's presence benefits not only the environment but also the local economy and social welfare, particularly for fishermen who depend on its fisheries.
Water flow for Wadaslintang Hydroelectric Power Plant: Balai PSDA Probolo
Fishing activities in Wadaslintang, both traditional and through FNC aquaculture, are key drivers of the local economy. Fish species such as tilapia, pangasius, catfish, marble goby, and Java barb are important commodities marketed not only locally but also to other regions. For the community, especially those who rely on fishing, the reservoir is a primary source of livelihood, making its management critical for their well-being.
History of Wadaslintang Reservoir
The feasibility study for the construction of Wadaslintang Reservoir was conducted in 1976 by the American company ECI Group, funded by a loan from the Asian Development Bank (ADB). After completing the study, ECI designed the dam and irrigation system from 1978 to 1980. Construction began in 1982 with the involvement of Hydro Resources Contractor Corporation (HRCC) from the Philippines and Brantas Abipraya, an Indonesian construction company.
During construction, the Medono River, the reservoir's main water source, was diverted through a 729.7-meter-long tunnel. However, a landslide during tunnel construction caused significant damage to a truck inside. Despite challenges, the main dam was built using compacted clay in wet conditions, similar to the Monasavu Dam in Fiji, a technique that was endorsed by Indonesia's Irrigation Director at the time, Ir. Soewasono.
In March 1987, the reservoir began filling with water, and by February 1989, it was officially used for irrigation after reaching a height of 185 meters. However, in 1999, a 2-meter subsidence at the dam's crest was detected, prompting repairs to restore its original height and ensure its continued function for irrigation and water supply.
Wadaslintang Reservoir irrigates around 31,634 hectares of farmland, with crops following a paddy-paddy-palawija (secondary crops) rotation. Its irrigation system is designed with consideration of downstream rivers such as Luk Ulo, Kalijaya, Kedungbener, and others, ensuring efficient water distribution. In addition to irrigation, the reservoir helps control flooding over 3,000 hectares, particularly in the Wawar region and supports a 16 MW hydroelectric power plant.
Fisheries potential at Wadaslintang Reservoir
Fishing is one of the primary economic activities in the reservoir. Local fishermen rely on fish resources for both daily sustenance and for sale in various markets. Commonly caught fish include tilapia (Oreochromis niloticus), pangasius (Pangasius hypophthalmus), marble goby (Oxyeleotris marmorata), Java barb (Barbonymus gonionotus), and African sharptooth catfish (Clarias sp). Fishermen typically use cast nets, which are effective in the large waters of the reservoir.
Tilapia farmed by local residents around Wadaslintang Reservoir
The fish population in Wadaslintang Reservoir is supported by an annual restocking program, where fish fingerlings are released to maintain the reservoir's fish resources and prevent overfishing. This initiative is a collaboration between Indonesia's Ministry of Marine Affairs and Fisheries (KKP), the Livestock and Fisheries Department of Wonosobo Regency, and local fishermen. The restocking program ensures a sustainable fish supply by preventing population decline due to excessive fishing.
The main fish species prioritized in this program include tilapia, Pangasius, marble goby, Java barb, and bonylip barb. Among these, tilapia dominates due to its high market demand and adaptability to changing reservoir conditions. Its rapid growth rate also makes it the most cultivated species in floating net cages at Wadaslintang Reservoir.
Aquaculture in floating net cages (FNC)
In addition to traditional fishing, aquaculture in FNC has become an important source of income for some fishermen at Wadaslintang Reservoir. Although the number of fishermen involved in FNC farming is relatively small, this activity significantly contributes to the local fishing economy. FNC provides an alternative way for fishermen to boost their income while making optimal use of the available water resources.
Tilapia is the most commonly farmed species in FNC. Its advantages include relatively fast growth and high adaptability to changing reservoir conditions. Moreover, tilapia is highly resistant to various diseases, making it an ideal choice for intensive farming. This fish also has substantial economic value, both in local and regional markets, offering profitable opportunities for fish farmers.
In addition to tilapia, pangasius is also farmed in the FNC system at Wadaslintang Reservoir, though in smaller quantities. Known for its high-quality flesh, pangasius is popular with consumers, but farming it poses more challenges compared to tilapia. Successful catfish farming requires extra attention to feed management and water quality maintenance, demanding specialized knowledge and skills from the farmers.
Beyond local efforts, a private company, PT Aquafarm Nusantara, previously operated FNC aquaculture at Wadaslintang Reservoir. PT Aquafarm Nusantara, a Swiss-owned company established in Indonesia in 1988, focused on developing and exporting tilapia. Headquartered in Klaten, the company ran fish hatcheries in Klaten and Sleman and used various large reservoirs in Central Java, including Wadaslintang, for growing tilapia, alongside other locations like Gajah Mungkur Reservoir in Wonogiri and Kedung Ombo Reservoir in Grobogan.
However, PT Aquafarm Nusantara’s operations at Wadaslintang came to a halt in early 2020 due to two major factors: an upwelling event and the impact of the COVID-19 pandemic. Upwelling, a phenomenon that brings toxic compounds to the water surface, led to mass fish deaths, while the pandemic added further economic and logistical pressures on the company. As a result, PT Aquafarm ceased all aquaculture activities at Wadaslintang and several other locations.
After PT Aquafarm’s closure, many former aquaculture technicians who had worked with the company used the knowledge they gained to start their own independent tilapia farming businesses. The expertise they acquired from Aquafarm, which operated according to international standards, became a valuable asset for their success in developing FNC tilapia farming, catering to both local and regional markets.
The sight of aquaculture in floating net cages at Wadaslintang Reservoir remains a key feature of the area’s fishing landscape
Challenges and efforts in sustainable fisheries management
Despite its significant potential in the fisheries sector, Wadaslintang Reservoir faces several major challenges in managing its resources sustainably. One of the primary concerns is the threat to the aquatic ecosystem's balance, often caused by overfishing and declining water quality. Unregulated fishing activities can lead to a decrease in fish populations, especially economically valuable species such as tilapia and pangasius. This reduction not only jeopardizes the sustainability of fish resources but also threatens the livelihoods of fishermen who depend on these catches.
Another significant issue is the phenomenon of upwelling, where colder water from the bottom of the reservoir rises to the surface during long dry seasons. This phenomenon has been a persistent threat to fish farmers at Wadaslintang Reservoir in Wonosobo, Central Java. Upwelling events have led to the sudden death of tens of tons of farmed fish in floating cages, affecting both local farmers and private companies like PT Aquafarm Nusantara. In some cases, up to 95% of fish in a single cage can perish, dealing a heavy blow to those who rely on aquaculture for their livelihoods.
Upwelling occurs when surface water temperatures drop significantly, causing warmer water from the reservoir's depths to rise. Along with the warmer water, toxic compounds trapped at the bottom also ascend, resulting in a sharp decrease in oxygen levels near the surface. This oxygen deficiency makes it difficult for fish in the cages to breathe, leading to mass die-offs. Such events pose serious challenges for managing the aquatic ecosystem in Wadaslintang Reservoir, especially during extended dry seasons.
To address these challenges, the local government, through the Wonosobo Fisheries Office, has implemented various efforts to promote sustainable fisheries management. A key initiative is regulating fish catches by enforcing fishing quotas and restrictions. Additionally, fisherman education programs have been a central focus, aiming to raise awareness among local fishermen about the importance of preserving aquatic ecosystems. One such effort is an annual restocking program, where fish species, including tilapia and pangasius, are released into the reservoir to help sustain fish populations and restore the ecosystem, which may have been impacted by overfishing.
Beyond restocking, the government actively provides training to both capture fisheries and aquaculture farmers. This training covers environmentally friendly fishing techniques and sustainable aquaculture practices. These efforts are intended to support the long-term sustainability of fish resources in Wadaslintang Reservoir, benefiting the local community while preserving the reservoir’s biodiversity.
Social and economic impact on local communities
Wadaslintang Reservoir serves as a critical hub for fisheries and aquaculture, delivering significant social and economic benefits to the surrounding communities. Many residents rely on fisheries-related activities, whether as fishermen, fish farmers, or workers in supporting industries. These activities not only provide a source of income but also create jobs, improving the overall well-being of the local population.
Local shops selling tilapia around Wadaslintang Reservoir
The aquaculture industry, particularly through FNC, also presents entrepreneurial opportunities for residents to develop more modern fisheries businesses. While the number of FNC farmers is lower than that of captured fishermen, the profit potential from farming fish, especially tilapia, is quite promising. tilapia farmed in FNC systems is in high demand in local markets, and there is even the potential for exports beyond the region and internationally. This success not only boosts the income of fish farmers but also strengthens Wadaslintang Reservoir’s position as a competitive fisheries center at both national and international levels.
Beyond fisheries, Wadaslintang Reservoir holds great potential as a tourist destination. The beauty of the reservoir and the surrounding fisheries activities attract visitors interested in seeing firsthand how fishermen work or enjoying fresh catches from the reservoir. Developing tourism centered on fisheries could provide additional income for local communities while showcasing the region's potential to visitors.
