Founded in 1941, the ‘Strandwerkgemeenschap’ aims to promote the study of marine biology, and in particular the flora and fauna of the Dutch coast. The organisation keeps a register of observations of fauna and flora, mostly made by experienced citizen scientists. Methods of data entry varied. Different observers and registrars acted on different perceptions and preferences, and uniformity in notations of taxonomy, place of observation, life stage of the object and additional descriptions of the observation was often lacking. A total of 98,360 sightings, made in the period 1921-2023, were streamed from an existing Excel spreadsheet into Darwin Core, subsequently checked, corrected and finally inserted into CB 4.0 Obs, a module developed for this purpose with easy connectivity to NLBif's Integrated Publishing Tool (IPT). The following data were noted and recorded in the CB 4.0 Obs database: taxonomic classification, scientific name, vernacular name(s), observation date, observer(s), identifier(s), country, province, locality, decimal coordinates, occurrence remarks, and event remarks. Taxonomy is based on the GBIF taxonomic backbone. The data consists of various groups of marine invertebrata including Mollusca (56,390), Arthropoda (11,004), Cnidaria (4,100), Bryozoa (3,345), Echinodermata (2,968) and Annelida (2,169), and other smaller phyla. Also many sightings of fishes, cartilaginous fishes and marine mammals such as porpoise, white-beaked dolphin and striped dolphin were made. A total of over 3,000 different species were observed and recorded. Dutch coastal fauna and flora are undergoing rapid changes. An overview of observations of a wide range of species within a large temporal range, contributes to a better understanding and anticipation of future developments and environmental changes. The data can be found at https://doi.org/10.15468/72c3wq.