This work presents a study on the horizontal turbulent eddy diffusion for both inner part and shallow areas around of Rio Grande Harbor navigation channel, Patos Lagoon estuary, RS, Brazil. It was made through the monitoring of Rodamine ‘B’ dye using aerial photos and water samples. From the radiometric interpretation of aerial photos in concomitance with tracer concentration level measured on environment was determined two different diffusion modes, one into the navigation channel dominated by strong currents and other on shallow areas in agree with weak local hydrodynamics. The mean horizontal turbulent eddy diffusion (K) determined for whole event was about 10065 cm²/s. Into the channel was identified a crescent diffusion rate with relation to the diffusion time and advection length, meanwhile in shallow areas was identified one decelerated process. The same was observed to the along flow eddy diffusion (Kx) and cross flow eddy diffusion (Ky). It’s also verified which the longitudinal eddy diffusion (Kx) varied from two to three times higher than transversal eddy diffusion (Ky) all process long. In shallow areas was also identified a eceleration on ratio between Kx and Ky. This behavior suggests one more important dispersion process into the channel when compared with the marginal areas.