Within the relatively recent past, many works of man have been constructed in estuaries and in their fresh-water tributaries in the interest of improving navigating conditions, or regulating the river flow for hydroelectric power generation and (or) flood control. In some cases such works have produced major and sometimes undesirable changes in the hydraulic, salinity, and shoaling characteristics of the estuaries involved. The undesirable effects have in some cases been so drastic that the overall effects may have been detrimental rather than beneficial. The works of man have influenced the hydraulic, salinity, and shoaling regimens in the passes of the Mississippi River, the lower Savannah River, and Charleston Harbor. The histories of these changes strongly recommend that any proposed changes should be thoroughly evaluated by all practicable means before their implementation to insure that the proposal will be beneficial to the system as a whole.