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Castanhão Reservoir Carrying Support Project

Fish Cages at Castanhão Reservoir

Fish production within water supply reservoirs is an important socioeconomic activity, but it causes pollution due to the significant release of nutrients into the water. This project developed a new tool that has assisted government in making decisions regarding the permitted input loads of nutrients from fish farms. Before the project, there was no methodology to predict the permitted pollutant loads for a sustainable management of reservoirs located in tropical semiarid regions. The hope is to propose measures to mitigate nutrient concentration in the reservoirs, such as a plan to increase sanitary coverage in the cities upstream the reservoir, as well as the use of better feed to optimize fish farming, and the use of new technologies to control the nutrient load from sediments, such as artificial aeration at the bottom of the reservoirs.

Innovation Summary

Innovation Overview

Fish-cage production in water supply reservoirs represents one of the most fast-growing aquaculture techniques in developing countries. However, it causes nutrient overloading. In this context, the nutrient carrying support capacity for fish production has been widely addressed worldwide, referring to the maximum quantity of fish that can be produced without triggering an environmental degradation process. Even though it is a methodology widely applied to temperate regions, before the present project, there was no methodology that could be used in tropical semiarid areas, such as the Brazilian Northeast.
During late 2000’s, Castanhão dam, the largest reservoir for multiple purposes in Latin America, was the largest fish producer in Brazil. Despite its large size, the aforementioned dam has shown a process of progressive degradation of water quality, evolving over the last ten years from oligotrophic to eutrophic. This has been attributed not only to the massive external and internal sources of nutrients to the reservoir, but also to the severe and prolonged drought event that occurred recently (2012-2018), which promoted a reduction of the reservoir volume to only 2% of its capacity. The combination of these factors significantly impacted water quality, resulting in an abrupt increase in water treatment costs for human, agricultural, and industrial water supply, as well as in recurrent kills of thousands of tons of fish in cages.
The present innovation is a result of a joint effort involving three main institutions: Water Resources Management Company (COGERH), Federal University of Ceará (UFC), and Ceará State Research Foundation (FUNCAP). The project, entitled Castanhão Reservoir Carrying Support Capacity Project, consisted of long-term (2021-2024) field/laboratory studies, mathematical modelling, and several meetings including local, regional, national and international public and private institutions related to the sector of water resources. The project aims to develop a new computational tool that will assist in decision-making by managers and water users regarding the quantity of nutrients that a reservoir located in a tropical semiarid region can receive without significant changes in water quality and preventing fish kills.
The developed computational tool has already being applied by COGERH to regulate the fish farm activities in the Castanhão reservoir, as well as to plan other mitigation measures to be implemented both at the watershed and reservoir scales. The computational tool and proposed methodologies are directly applicable to the other reservoirs located in the Brazilian Northeast. This has been supported by the National Water Agency (ANA), who has participated in several project meetings. Additionally, the proposed innovation can also be applicable to other similar regions in Australia, USA and Africa, for instance, as it has also been discussed and validated by many international institutions (USGS, EPA and IGB Berlin).

Innovation Description

What Makes Your Project Innovative?

The Castanhão Reservoir Carrying Support Project is an innovation in water resources because for the first time extreme environmental conditions, which are characteristic of tropical semiarid regions, such as droughts, are considered in the process of quantifying the permitted loads from fish-farming and other activities. Furthermore, this project provides an easy-to-interface computational tool that allows assist in water resources management, coupling hydrology and water quality. Moreover, this project also considers through an innovative way the internal nutrient (phosphorus) load that is released from the bottom of the reservoir under low oxygen conditions. Overall, this project incorporates all the processes that affect nutrient concentrations in reservoirs under two climatic conditions (dry and rainy seasons), as well as during drought events. More details of the innovative nature of the project can be found in the journal papers listed in Section 7 - Materials.

What is the current status of your innovation?

Field surveys, laboratory analyses and computer model development/improvement will be carried out until April/2024, when the final project presentation and discussion will be conducted together with the different institutions, fish farmers and other water users involved. Furthermore, a computer program is being developed to provide an user-friendly interface for use by water managers. We have also been planning a second phase of the project, in which we intend to replicate the methodology and apply/refine the computer tool to 10 additional strategic reservoirs in the state of Ceará. The idea is to propose measures to mitigate nutrient concentration in the reservoirs, such as a plan to increase sanitary coverage in the cities upstream the reservoir, as well as the use of better feed to optimize fish farming, and the use of new technologies to control the nutrient load from sediments, such as artificial aeration at the bottom of the reservoirs.

Innovation Development

Collaborations & Partnerships

COGERH has performed water and sediment sampling, laboratory analyses, and hydrologic measurements in the watershed and reservoir. UFC has developed/validated the model to predict the dynamics of water quality in the reservoir and is working on the development of the computational tool that will be used to assist water management. UFC has also conducted specialized laboratory analysis. Fish farmer association and Ministry of Aquaculture have provided data on the fish production and feed.

Users, Stakeholders & Beneficiaries

The innovation will primarily benefit the fish farmers who are located inside the reservoirs, as the carrying support knowledge will guide the best-management practices for the activity and potentially reduce the number of fish kills. The water treatment companies and industries will also treat a raw water with better quality, thus reducing the water treatment costs. Finally, water resources management companies will also minimize the conflicts among water users in committee meetings.

Innovation Reflections

Results, Outcomes & Impacts

One of the main results of this project is the creation of an integrated database including hydrologic, water quality and sediment data for the largest multiple-use reservoir in Latin America. Another outcome is the development of a computational tool to evaluate scenarios and propose alert systems not only to prevent kills, but also to improve water management for other water users, bringing water quality dynamics to water resources management, through a new methodology adapted to tropical semiarid regions, with the feedback from institutions and society. This project also has been qualified human resources through various master's and doctoral projects, in addition to the publication of international scientific papers (see Section 7).

Challenges and Failures

The biggest challenge was bringing together all the stages of the project to produce and discuss the main results. The fish farmers, at beginning, did not believe in the proposal and a lot of fake news was published, so trying to convince them and show that they would be the major beneficiaries was challenging. Furthermore, gathering field data at a large scale, training personnel for specialized laboratory analyses, carrying out sophisticated computational analysis and promote an efficient water management administration through this project was also challenging. Finally, bringing together and continuously updating all this information into a computer program continues to be challenging.

Conditions for Success

For the success and continuity of this project, it is essential to have the operational support of the Water Resources Management Company, making monitoring more frequent, thus making the computational tool increasingly accurate. The high degradation of Brazilian semiarid reservoirs is a reality, and water quality management must be a priority, incorporating not only the company's infrastructure, but also all human resources trained during this project. The increasingly accurate model, under different water quality conditions (more years), will tend to reduce environmental problems resulting from water quality degradation, for example fish kill cases.


There are several other Brazilian states and regions around the world (Australia, parts of Africa, China, USA, for example) with similar environmental conditions of seasonality/water scarcity, as observed in Ceará, in the Brazilian semiarid. Through this project, we can replicate the same methodology offering adaptations in the case of larger/smaller reservoirs and/or with permanent/intermittent water flows. This project has already been discussed in several conferences and meetings with other global environmental agencies (USGS, EPA, ANA). Moreover, its main results have been published in peer-reviewed journals (see Section 7). This suggests that the innovation has a potential to be incorporated by other countries or regions.

Lessons Learned

The collaboration involving research institutions, governmental agencies, and society, also including broad discussions with the national and international community, has a great potential to promote scientific/technological advances in the field that result in effective improvements in water resources management. The political, technical and financial support from the water resources management company also allowed the university group to reach higher levels of research findings, technological development and practical application of the results. Additionally, the involvement of undergraduate and graduate students in the activities also contributed for a better human-professional formation and to the feasibility of the project.


  • Implementation - making the innovation happen

Innovation provided by:



Date Published:

5 June 2024

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