The hydrologic regime of the Illinois River has been substantially altered by locks and dams, floodplain levees, water diversion, and development of the watershed over the past 100 years. The natural flood pulse, a fundamental rhythm to which the plants and animals of both the river and its floodplain had adapted, has been disrupted. State, federal, and non-governmental organizations are currently trying to naturalize the Illinois floodplain-river system. Little, however, is known about how to recover those elements of the flood pulse essential to the native biota. In this study we propose moist-soil plants, whose life history is dependent upon flood pulsing, as ecohydrologic indicators of the flood pulse. We explain how moist-soil plants are supported by the natural flood pulse and present a conceptual framework that links the flooding regimes of the river and the reproductive success of the plants. Successful germination and full growth of moist-soil plants can be a useful indicator for optimum naturalization of flood regimes. The framework also shows how the interdisciplinary linkages between hydrology, ecology, and spatial analysis assist in predicting, measuring, and comparing consequences of alternative naturalization scenarios. A new ecohydrologic parameter, lowest elevation for successful moist-soil plant production, is presented.