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Watershed studies conducted in the 1960's and early 1970's throughout the U.S. found dramatic increases (3-15oC) in stream temperature due to clearcut riparian timber harvest and site preparation activities. These findings were a major impetus to the passage of streamside protection regulations in most western states in the 1970's, and development of Best Management Practice (BMP) programs elsewhere. Yet today, thousands of stream miles in forested watersheds, particularly in the Pacific Northwest, fail to meet water temperature criteria under the Clean Water Act, and Total Maximum Daily Loads (TMDLs) are being actively prepared. While several studies have found streamside buffers that maintain shade can be an effective way to prevent adverse temperature changes, little manipulative research has been conducted to thoroughly evaluate the effectiveness of current state programs. Our study examined reach-scale temperature changes due to harvesting at 10 sites in western Montana that were harvested under the states Streamside Management Zone regulations. Temperature loggers were placed at the upstream and downstream boundaries of planned harvest treatments. Data were collected for at least one summer before and after logging. Results show that increases in maximum summer temperatures over 1oC were uncommon, with most sites having undetectable changes. While impacts to stream temperature from historic practices may persist, it appears that streamside buffers retained under Montana law are effective at preventing adverse temperature changes. There are several similar studies presently underway throughout the U.S., which should provide additional information on the effectiveness of state programs in coming years.