Deltas are complex systems where tidal and riverine signals interact with each other. In river-dominated deltas, where river discharge is sufficiently high, tidal amplitude is attenuated and distorted. Here we use wavelet analysis to examine the water level signal in stations located in wetlands adjacent to the main river outlet in the Wax Lake system, part of the Mississippi River Delta in Louisiana, USA. We study the signal attenuation in lateral wetlands at different frequency bands, following the propagation of the water level signal from the Gulf of Mexico to the innermost stations. During high river discharge, the astronomical tide measured inside the wetlands is reduced of 90%–98% in comparison to the tide in Atchafalaya Bay. Storm surge events, largely occurring at lower temporal frequencies, propagate conserving their energy once the signal enters the delta mouth. The river discharge signal, mostly present at frequencies lower than 1.59 μHz, is felt depending on river discharge conditions and the station position within the wetlands. Our results suggest that lateral wetlands in the Wax Lake system act as a low pass filter, attenuating tidal components but not the low frequency components of storm surges.