Mariculture provides an increasing seafood supply to a growing population. It also brings unintended consequences for the environment, resources, and sustainable development. In an attempt to evaluate the impacts of intensive mariculture of lobster in cages, the water quality and sediment quality in three South-Central regions of Vietnam, Xuan Dai Bay, Van Phong Bay, and Cam Ranh Bay, were monitored from April 2019 to May 2020. In each bay, two stations in the farming areas were compared to a non-farming reference station. The result showed no significant differences in the water quality parameters among the stations within each bay and between the bays. However, sediment quality noticeably differed between sites within each bay and between the bays. The accumulation of the observed parameters of sediment in farming areas was higher than in non-farming areas. In the Cam Ranh Bay, the concentration of organic carbon, total nitrogen, and total phosphorus in the sediment in farming areas was approximately 1.4 times higher compared to non-farming areas. Similar results were found in Van Phong Bay and Xuan Dai Bay with different magnitudes. Additionally, the difference in the sulfide concentration in the sediment of Van Phong Bay was notable for its better environmental quality than the other two. The findings indicated that mariculture wastes would accumulate in the sediment, and decompose over time, causing sediment degradation, which may affect the benthic biota in coastal waters.