The expansion of cage aquaculture in large hydroelectric reservoirs requires assessments that ensure an accurate and technically grounded environmental analysis of its impacts, promoting sustainable management practices. This study aimed to evaluate the effects of this activity on water quality in the Itaipu Reservoir by analyzing the spatial and temporal heterogeneity of limnological variables, represented by the Trophic State Index (TSI). Monitoring was conducted over four years, covering periods before and after the implementation of a tilapia (Oreochromis niloticus ) cages aquaculture system at the Ocoy aquaculture park.
The study area is located on the Brazilian shore of the Itaipu Reservoir, where an aquaculture system with 30 cages of 6 m³ each was implemented. To assess the effects of tilapia production, limnological data were collected at four points: in the center of the aquaculture area (Net-pens), 1,000 m upstream (Upstream), 1,000 m downstream (Downstream), and at a control station (Control), located outside the hydrodynamic influence of the aquaculture activity (Figure 1).
The TSI indicated low trophic levels, with 87.5% of samples classified as ultraoligotrophic and no significant differences between sampling points (p = 0,6914). The lowest values occurred during the farming periods, and the highest during non-production periods.
The results indicate that the implementation of cage aquaculture in the Ocoy did not cause significant changes in the trophic state of the water, as evidenced by the low average TSI values and the absence of statistical differences between monitoring points. The predominance of ultraoligotrophic conditions throughout the evaluated period, including during production cycles, suggests that under the adopted operational conditions, the aquaculture activity had a limited environmental impact on the water quality of the Itaipu Reservoir.