Erosion threshold (n=5) of surface sediment was measured with a cohesive strength meter (CSM Mk IV) to determine seasonal and spatial changes in sediment erodibility at Nazareth tidal flat and marsh located west of Rimouski on the southern shore of Lower St. Lawrence Estuary (Canada). Multiple field campaigns were conducted at three cross shore transects (A, B, C) in summer 2016 (8, 9, 10 August), summer 2017 (23, 24, 25 August), with subsequent campaigns at B Transect in autumn 2017 (22, 25 November), winter 2018 (16, 20 February), spring 2018 (30 May), and summer 2018 (6 September). The data presented here does not contain the summer field campaigns, which was published in the context of annual variations in sediment erodibility (Waqas et al., 2019, https://doi.org/10.1594/PANGAEA.911769).