overflow channel system, and the condition of riparian vegetation. Lateral change in the channel—meandering—is an essential feature of streams in alluvial valleys, yet we have systematically attempted to straighten and confine rivers in an attempt to increase water conveyance, confine flows, and protect property. Recent large floods, however, serve to remind us that dams and levees have limits and cannot contain increasingly large floods that occur at least in part as a result of watershed and floodplain alterations.
Recognize that dams change rivers and their ecosystems, but some of the negative consequences of dams can be mitigated through operational strategies that create more normative discharge and temperature regimes. Dams can alter seasonal availability and temperature of water extensively, reducing stream productivity and diversity. Large, erratic base flows create a dead zone along the river margin where plants and animals are either washed away or desiccated and reduce near-shore shallow water habitat that is crucial for juvenile fishes and emerging insects. Simply establishing minimum flows as mitigation for lost habitat or extirpated species is insufficient to maintain the physical and biological integrity of rivers. Periodic flushing flows are needed to scour river bottoms, build gravel bars, replenish woody debris, and also minimize proliferation of nonnative biota. It is also important to reduce the erratic nature of base flows associated with daily hydropower operations and irrigation withdrawals. Restoration of more natural discharge regimes in regulated rivers and lakes is one of the most pressing needs in maintaining normative watershed conditions.
Conserve and promote native species by creating native biota reserves, restoring and reconnecting critical habitats, and minimizing conditions that favor invasions of nonnative species. Native biota can serve as sentinels of ecological change and reductions in the abundance of native species can indicate degradation. Watershed planning can incorporate steps to protect and even restore habitat, including designating reserves for remaining intact assemblages of native plants and animals (Moyle and Yoshiyama, 1994; Sedell et al., 1994) and is especially suited for mobile organisms that require a network of interconnected habitats.
Promote best management practices for upland and riparian land uses as a means of controlling pollution, but recognize that the best practices for one watershed in one region of the country may differ from other watersheds in other regions. Many agencies and organizations, including the U.S. Department of Agriculture, have implemented a variety of forestry, grazing, and agricultural initiatives to limit water pollution and loss of biodiversity. Rigorous scientific evaluation of best management practices is required, however, before they are widely accepted in place of legal standards (Bisson et al., 1992).
Implementation of the 1972 Clean Water Act (CWA) has had profound impacts on state and federal regulatory programs related to water quality and on