## 5 Conclusions  
The radargrams identified a depression in Area 1 (Braganca), which appears to have been filled with material at some time in the past. A compacted layer was also detected near the surface, although no evidence of a water table was found at this site. In Area 2 (Tracuateu), the GPR prospection identified a horizontal reflector (6-6.5 m) corresponding to the water table, which was confirmed by a well drilled on the property. Two other features recorded at this site were a stack of horizontal layers approximately 1 m thick and hyperbole-shaped reflectors that may represent the presence of buried pipes. The EMI survey identified the soils in both study areas, at depths of up to 7.5 m. The characteristics of the soils of both areas were found to be appropriate for fish farming. In Area 1, the Horizontal Dipole (HD) with the antennas at 10 m intervals recorded low levels of conductivity, between 3.5 and 17 mS.m\({}^{-1}\), which indicate the presence of a clayey subsoil. In Area 2, conductivity was between 16 and 48 mS.m\({}^{-1}\), which also indicates the presence of a clayey substrate. The preliminary sedimentological analyses identified clayey soils (23-60% clay) in Area 1 and very clayey soils (60-100% clay) in Area 2, which confirmed the lithology of the subsoil identified using the EM34-3 electrical conductivity meter. The dielectric characteristics and the propagation velocities of the electromagnetic (EM) wave determined the lithology of the principal strata of Area 1, which were validated by the SPT probes. The combined (GPR + EMI) geophysical approach permitted the acquisition of valid, complementary data on the subsurface that provide reliable information on the characteristics of the soils of the study areas earmarked for the installation of aquaculture projects. Based on these findings, we would recommend the integrated application of GPR and EM34-3 tools, combined with sedimentological analyses and the SPT, for the diagnosis of the characteristics of the subsoil of areas earmarked for aquaculture projects. This approach will guarantee the data needed to evaluate the configuration of the subsoil, which may be fundamental to ensure an adequate decision-making process during the development of aquaculture projects, by both minimizing the environmental impacts and guaranteeing the maximum economic returns of the operation. This type of approach can also be applied to the evaluation of the sites of small dams, tailing pits, mud pits, water holding installations, and even wildlife refuges. In the case of deeper geology, however, the use of Electrical Resistivity Tomography (ERT) is recommendable. Even so, a more detailed analysis would require the complementary use of lower-frequency GPR. Ground Penetrating Radar can also be used to obtain bathymetric data and bottom stratigraphic sediment profiles from natural freshwater environments, such as rivers and lakes. This freshwater GPR technique cannot be used in salt or brackish water environments. Future studies may benefit from the use of high dynamic range GPR with a built-in GPS and integrated odometer, to minimize spatial distortions during data collection, which ensures the quality of the data for processing. Conceptualization, R.W.T.P., P.A.C.O., and F.A.A. ; Methodology, R.W.T.P. and P.A.C.O. ; Validation, R.W.T.P., P.A.C.O., and F.A.A. ; Formal Analysis, R.W.T.P., P.A.C.O., and F.A.A. ; Investigation, R.W.T.P. and P.A.C.O. ; Resources, R.W.T.P. and P.A.C.O. ; Data Curation, R.W.T.P. and P.A.C.O. ; Writing--preparation of original draft, P.A.C.O. and F.A.A. ; Writing--Review and Editing, P.A.C.O. and F.A.A. ; Supervision, P.A.C.O. and F.A.A. ; Project Administration, P.A.C.O. All authors have read and agreed to the published version of the manuscript. **Funding:** Dean of Research and Graduate Studies-PROPESP/Federal University of Para-UFPA (Brazil). [PERSON] is a CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil) research fellow. **Institutional Review Board Statement:** Not applicable.