Phase I of the Colorado River Water Availability Study (the Study or CRWAS) provides an unprecedented foundation for water resources planning in Colorado. The Study, which began in 2008, combines the data and models developed by the CWCB and the Division of Water Resources over the last 15 years with new information on past droughts and wet spells and possible future changes in climatic conditions to produce the most comprehensive look to date at the Colorado River water supply in our State. Phase I of the Study provides a strong foundation for subsequent work, which will examine water availability for future water supply projects and for additional non-consumptive water needs. The Study is guided by extensive public involvement and provides a transparent examination of complex water management issues and the data, science, and computer tools applied to assess these issues. With the publication of this report and the launch of the CRWAS on-line data viewer, Colorado's water community can now fully utilize this Phase I assessment of water availability for our current supply systems and levels of water demands. State agencies and Colorado River stakeholders can now prepare for further assessments of water management strategies to meet future demands and investigate the risks associated with each of them.