This dataset reports the responses of annual river flow to forestation in 43 catchments and contains 770 data points. Data shows the change in river flow following forestation at annual time scales, along control river flow measurements and associated metadata from primary and secondary sources. Data collection, processing and interpretation were performed by Laura Bentley and David A. Coomes between January 2018 and October 2019. Forestation was defined as a change in land cover from a stable, non-forested state to a forested one, independent of the long-term history of forest cover. Paired measurements of annual river flow following forestation (mm) and river flow under control land cover conditions (mm) are provided for each year that the catchment dataset satisfied our inclusion criteria. River flow response is provided as both an absolute difference (mm) and as a percentage of control flow in the same year. Estimates of catchment annual precipitation, annual potential evapotranspiration, forest age, forest area, and the year of study are provided for each river flow response data point. Metadata are provided concerning catchment land cover history, land use history, catchment area, forest type, average climate and the method of forest establishment. The dataset contains catchments that were planted with trees and catchments in which forest cover regenerated without planting. Historical forest cover was reported in some catchments, and not reported in others. The 43 catchments a distributed unevenly across the globe, in 13 countries. The length of time series for each catchment varies from 2 years to 57 years, with and average duration of 19 years.