Why: Lake IJsselmeer is the largest freshwater body in the Netherlands and an important source of drinking water. Like other freshwater ecosystems, it experienced a peak in eutrophication during the 80s, after which nutrient loads began to decline (Frenken et al., 2023). Very little is known about the trophic history of Dutch freshwater ecosystems prior to the invention of synthetic fertilizer. To assess the success of water quality measures, restoration efforts, and set realistic targets, we need to reconstruct historical conditions using sediment cores.