This study assessed the environmental impact and carrying capacity of aquaculture in the Tekoha Ocoy Aquaculture Park, Itaipu Reservoir (Paraná/Brazil), using hydrodynamic and water quality modeling focused on phosphorus as the key impact indicator.
A hydrodynamic model (Delft3D) was applied to calculate the residence time in the Ocoy River embayment , based on bathymetry, wind, reservoir level variation, and river flows. The Dillon and Rigler equation was used to estimate the maximum allowable phosphorus load, and scenarios were simulated according to aquaculture sizes defined by regulation.
The hydrodynamic model estimated an average residence time of 196 days for the aquaculture park. Based on this, the maximum allowable phosphorus load was calculated at 25,69 tons of P/year, supporting a maximum fish production of 1. 338 tons/year for Oreochromis niloticus.
Phosphorus concentration simulations revealed an initial increase across all scenarios (figure 1) , likely due to low tributary flows and reduced reservoir levels. In every case (figure 2), concentrations exceeded the legal limit of 0,005 mg/L, particularly in medium and large-scale operations, which require individual assessment in areas with long residence times.
However, the spatial impact remained localized. As shown in Figures 1 and 2, the effect radius did not exceed 300 meters from the center of the aquaculture area. Notably, small-scale aquaculture, despite initial exceedance, showed a decline in phosphorus levels after the first year, stabilizing within legal limits for the remainder of the simulation. This scale of production is therefore strongly recommended for sustainable development in the reservoir.