This dataset was collected in support of a study on the resilience of restored seagrass (Zostera marina) meadows to marine heatwave exposure in North Wales, United Kingdom (Thomas et al., 2026). It provides intertidal quadrat survey data recording seagrass shoot and reproductive shoot density, rhizome presence, canopy height, percentage cover of seagrass, epiphytes and algae, and sediment redox potential, pH and temperature, collected during repeated monitoring visits to four restored seagrass sites between June 2023 and October 2025.