What does "nature" mean? This general question, central to the social construction of nature, is addressed here by examining one of nature's particulars, Pacific salmon, and by looking at how one group of people, salmon biologists, imbue the fish with meaning. Based upon historical, comparative, and qualitative data, it appears that nature is socially constructed through both cognitive and physical processes. "Salmon"- and indirectly nature - emerges not as a monolithic, timeless, certain entity, but rather as one that is manipulable, fleeting, and the product of a variety of social relations. In particular, public policy and economics appear to have profoundly influenced salmon biologists' cognitive and physical constructions of salmon.