Integration of agroecosystems with protected lands and waters is critical to the conservation of Earth’s biodiversity. Rice agroecosystems support many species by providing aquatic habitat where natural wetlands have been altered or drained. In the Sacramento Valley of California, rice fields and irrigation canals can be refuges during the dry season and periods of drought. We quantified the spatial scale and magnitude of the effect of rice growing on the growth and survival of the giant gartersnake (Thamnophis gigas), a threatened species that persists primarily in areas of rice agriculture in the Sacramento Valley. We analyzed capture-mark-recapture data from 19 populations of giant gartersnakes with an integrated growth-survival model and used distance-weighted covariates to account for the decline in influence of rice with increasing distance from our study sites. We found strong support for a positive effect of rice grown within 1.9 km of a canal on giant gartersnake growth. There was also support for a positive effect of rice on giant gartersnake survival, although the spatial scale extended out to 5 km or more. Our results demonstrate how active rice growing benefits giant gartersnakes inhabiting irrigation canals and demonstrate an approach for studying landscape effects on wildlife in agroecosystems.