Short-lived radionuclides (210Pb and 137Cs) were used to document sedimentation regime changes over the last ∼100 years, from analysis of a single sedimentary sequence collected in the coastal zone of the Gulf of Tehuantepec, South Pacific of Mexico. Sedimentation rates found in the core Tehua II-21 varied from 0.03 to 0.21 cm yr−1, whereas mass accumulation rates ranged from 0.05 to 0.29 g cm−2 yr−1. 137Cs data validate results obtained from 210Pb measurements and confirm significant changes in the sedimentation regime between 1950 and 1970. We associate these alterations to land use changes, including deforestation for agriculture development and industrialization, as well as the regimentation of the Tehuantepec River from the early 1960s to the late 1970s. This interval has been marked by a major demographic expansion that followed the industrial development of the area.