This dataset provides continuous monthly river flow series for 51 flow stations across the Island of Ireland, commencing in December 1766 and running to November 2016. Flows have been reconstructed using an Artificial Neural Network and the GR2M conceptual hydrological model. Reconstructions from the two models as well as their ensemble are presented for each flow station (ID provided in each column). Also presented are the 2.5 and 97.5 quantile values for the ensemble reconstruction series, which represent the upper and lower uncertainty bounds of the respective ensemble flows derived during the flow generation process.