Healthy and sustainable ecosystems provide a wide array of services to human communities, including improved water quality, protection from floods and storms, and provision of the food and fiber that we rely on as part of our everyday lives. Over time, human influences have degraded ecosystems to the point where it is difficult to appreciate how productive they can be. Freshwater ecosystems, including rivers, floodplains and estuaries, are among the most altered in the United States today. In fact, 98 percent of all rivers in the U.S. are now regulated by human interventions.
Ecosystems respond to changes in the patterns of river flows and water quality. Reservoir operations play a role in this because the presence of reservoirs and the
management decisions made at dams affect aquatic conditions for long stretches of river and connected wetlands. The fact that reservoirs affect ecosystems is also very powerful. It implies that reservoirs can be used as vital tools in the restoration and management of ecosystems.
Scientists and water managers have discovered and continue to refine our understanding of connections between river flows and healthy ecosystems. Periodic flooding and seasonal dry spells are now known to benefit the plants and animals that live in rivers, floodplains and estuaries because they nurture different parts of organisms’ life cycles. In turn, healthy populations of fish and other aquatic organisms support recreation activities, and vibrant river ecosystems provide cleaner water supplies for human communities.