Buying and leasing water rights for environmental protection is becoming an important method for protecting river and stream flows in the western United States. The region has experienced an increasing number of market transfers of water to protect water quality and fish and wildlife habitat. From 1990 to 1997, more than US$37 million was spent to lease 2 million acre-feet of water and US$23.8 was spent to purchase 132,000 acre-feet of water for environmental protection. State and federal agencies are responsible for most of these market transfers, but there is increasing activity on the part of private organizations to acquire water for instream needs. This paper examines recent developments of instream flow marketing in the western United States. The paper reviews recent transfers and acquisitions programs and discusses the growing entrepreneurial efforts by private organizations to acquire water rights for instream use. Market information including price and quantity of water traded was collected from market participants. The average purchase and lease prices for the region are US$397 and US$30 per acre-foot, respectively.