This article examines the role of ex post labor supply in smoothing income in response to crop losses caused by large floods among riverine households in the Peruvian Amazon, where rich environmental endowments permit a variety of resource extractive activities and coping responses. The paper finds that households respond to crop losses primarily by intensifying fishing effort not by relying on gathering of non-timber forest products, hunting, or asset liquidation. This ex post labor adjustment helps to smooth total income against small crop losses but less well against large crop losses. Both relatively non-poor households with better fishing capital and poor young households with a physical labor advantage employ this natural insurance in rivers.