Remote sensing plays an important role in the monitoring of inland waters. Recently, Cubesats have become an alternative data source for studies that require high spatiotemporal resolutions. However, the radiometric quality of those data was never evaluated for inland water studies. This letter presents the experimental results to assess the quality of the Remote Sensing Reflectance (Rrs) from commercial PlanetScope (PS) CubeSat constellation. The radiometric assessment was performed using in situ Rrs measured at 37 field stations on distinct lakes across Lower Amazon Floodplain. In turbid lakes, PS bands presented Rrs accuracy of 46% for all VNIR bands (coefficient of determination (R2 ) = 0.56), while in clear water lakes the results were not satisfactory (R2 = 0.08). Furthermore, results showed a spectral dependence in the quality of Rrs retrievals for the turbid lakes, with sounder metrics in visible bands (red band: R2 = 0.83). Finally, there is a high correlation between water quality parameters (sediments concentration and Secchi Depth) and PS Rrs at the red band (R2 > 0.74). Although PS images are mostly designed for land applications, the results suggest that the radiometric quality is sufficient for the monitoring of fine-scale mixing processes between river waters and floodplain lakes.