This article presents a scientific overview of the processes and the impact of environmental degradation of coastal waters due to human activities on the adjoining land. The direct effects range from eutrophication and harmful algal blooms, to hypoxia and anoxia. The indirect effects are more subtle and can also lead to the collapse of the ecosystem as in the case of coral reefs or seagrass meadows. Engineering solutions alone are not available to prevent this degradation that can only be reversed, or prevented, using a basin-wide ecohydrology approach.