Colíder HPP is an earthfill dam located at Teles Pires River in the northern region of Mato Grosso, Brazil. The dam, built and operated by Copel Generation and Transmission S.A., have a rated power production of 300 megawatts. Bubbles entrained during spill events in Colíder dissolve air into the water increasing total dissolved gas (TDG) concentration, which might cause gas bubble disease in affected fish. Reduced-scale laboratory models and a three-dimensional (3D) computational fluid dynamics (CFD) model were developed to understand the dynamics of spillway jets responsible for bubble entrainment at deep regions in the stilling basin where gas dissolution is enhanced. Two laboratory models were constructed in the CEHPAR/LACTEC in Curitiba, Brazil, a 1:120 scale hydraulic model comprising the entire Colíder tailrace and a 1:60 scale spillway sectional model. According to the literature, four typical jet regimes may occur due to the combination of the operational settings of the spillway and tailwater elevation: 1) plunging flow, 2) skimming flow, 3) undular jet and 4) surface jump. Plunging flow is undesirable since spillway jets plunge deep into the stilling basin increasing TDG levels. Skimming flow is the regime that results in the lowest TDG concentration downstream the spillway. However recent studies developed in computational models, pointed out that undular jet and surface jump jet regimes can also decrease TDG concentration of the downstream water. This paper presents details of the physical model studies. Several deflector geometries were tested for various combinations of flow discharges and tailwater levels, totaling 131 tests. The results showed that spillway jet regime in Colider is very sensitive to the geometrical and hydraulic conditions. The tests helped to build a deflector performance curve, which may be used to predict the flow pattern according to operational conditions in the spillway and powerhouse. The data led to a dimensionless plot to predict spillway jet regime as a function of deflector elevation, flow discharge and tailwater level. Results from this study guided the deflector design that was afterwards evaluated by IIHR-Hydroscience & Engineering, The University of Iowa using a computational two-phase flow model implemented in the open source code OpenFOAM.