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Refuge management may require manipulation of soil and water to produce habitat structure or essential foods. Production of foods does not assure that waterfowl will use them. Foods only are accessible if appropriate water depths are maintained during critical time periods, habitats are protected from disturbance, and habitats that provide protein and energy are close together. Disturbance is particularly important, and recognition of the influence of disturbance on access to and acquisition of needs throughout the annual cycle is essential. Subtle effects caused by bird watchers, researchers, and refuge activities during critical biological events may be as detrimental to waterfowl populations as hunting or other water-related recreational activities such as boating. At certain locations, predators or activities associated with barge traffic, oil exploration, or other industrial or military operations are detrimental.