"A skyscraper is as natural as a bird's nest" -Alan Watts. For millennia, people have altered freshwater ecosystems directly through water development and indirectly by global change and surrounding land-use activities. In these altered ecosystems, human impacts can be subtle and are sometimes overlooked by the people who manage them. This article provides two case studies near Boulder, Colorado that demonstrate how perceptions regarding these ecosystems affect their management. These examples are typical of lakes and streams along the Front Range of Colorado that are simultaneously natural and social in origin. Although natural, many of the region's freshwater ecosystems are affected by ongoing ecologic, hydrologic, chemical, and geomorphic modifications produced by human activity. People and nature are both active participants in the production of these freshwater ecosystems. The concept of "hybridity," borrowed from geographers and social scientists, is useful for describing landscapes of natural and social origin. Hybrid freshwater ecosystems are features of the humanized landscape and are derived from deliberate cultural activities, nonhuman physical and biological processes, and incidental anthropogenic disturbance. Our perceptions of "natural" freshwater ecosystems and what definitions we use to describe them influences our view of hybrid systems and, in turn, affects management decisions regarding them. This work stresses the importance of understanding the underlying societal forces and cultural values responsible for the creation of hybrid freshwater ecosystems as a central step in their conservation and management.

Timelines and Baselines 4 The First Americans and the Legacy of Coronado 5 Major Stephen Harriman Long and the United States Topographical Engineers 9 John C. Fremont and the Corps of Topographical Engineers 12 two Juggernaut of Change 19

The Preble's meadow jumping mouse (Zapus hudsonius preblei) and issues surrounding its listing as a federally threatened species provide a contemporary case study that contributes insights toward the construction of nature and the social construction of science. Designating the mouse as a subspecies and the attack on its taxonomic validity illustrates the contentious and uneven transfer of biological knowledge from the field of taxonomy to the public realm of environmental politics, regional development and species conservation. Listing the mouse set off a process where federal, state, and local governments, plus dozens of others spent millions of dollars and an extraordinary amount of time in a chaotic and often contentious mouse conservation effort. From naming the mouse to listing it under the Endangered Species Act (ESA), the author traces a chain of events that has affected both the landscape and institutions along the Colorado and Wyoming Front Range. This article shows how and why a political struggle over land use transformed into a scientific debate over taxonomy. It describes how economic forces and ideological perspectives influence taxonomists and the names they give plants and animals. In the western US, taxonomists are becoming key actors in struggles over access to riparian resources. The author discusses how using single species listings under the ESA as a tool to combat urban sprawl or to influence land use decisions undermine political support for both the ESA and other species conservation efforts.

Political ecologists use various approaches to understand the human-environment interaction and mechanisms for environmental change. An actor-centered analysis is one approach that can provide valuable insight to first world water resource issues by providing a deeper understanding of environmental change not available through traditional policy or resource analysis. In the case study described in this paper anthropogenically modified water resource systems can be seen as resulting from the actions of all the actors who are using and appropriating water and resources in the riparian corridor. The case study uses the Boulder Creek watershed in Colorado, USA to describe how the process of Euro-American settlement and development has permanently and irreversibly altered river hydrology, ecology, and geomorphology in many western North American watersheds. The observed character of streams today represents the cumulative result of the motivation and interactions, both collectively and independently, of the various actors who have appropriated water, extracted resources, and modified the environment to meet their various needs. With over 140 years of development, the streams in the Boulder Creek watershed bear little resemblance to what once existed. The water has been fully appropriated, lakes created where there were none, native riparian vegetation replaced or dominated by introduced species, and native fish species replaced by introduced species. Additionally, the stream channels have been bridged, channelized, modified by flood control structures, inundated by reservoirs, and encroached by all forms of urbanization.

Timelines and Baselines 4 The First Americans and the Legacy of Coronado 5 Major Stephen Harriman Long and the United States Topographical Engineers 9 John C. Fremont and the Corps of Topographical Engineers 12 two Juggernaut of Change 19