A significant barrier to economically efficient management of most reservoir systems is lack of reliable information about how recreational values change with reservoir levels. This paper presents evidence on marginal values of water for recreation at Corps of Engineer reservoirs in the Sacramento, California, District. Data on visitors were collected by origin and destination before and during the early part of the 1985--1991 California drought. Because lake levels varied widely during the sample period, water's effect on visits was isolated from price and other effects. An estimated regional travel cost model containing water level as a visit predictor provided information to compute marginal values of water in recreation. For the range of the lake levels seen, annual recreational values per acre-foot (1234 m3) of water vary from $6 at Pine Flat Reservoir to more than $600 at Success Lake. These findings are limited to use values of visitors who travel to the reservoirs and do not reflect passive use values to people who value the reservoirs but never visit them. Analysts could apply similar methods to other river basins in which a public agency controls the management of multiple water uses. ¿ American Geophysical Union 1996