On the island of Lolland, southeast Denmark, an area of almost 300 ha is currently under archaeological investigation prior to the planned construction of a tunnel between Denmark and Germany under the Femern belt. The area investigated in the context of the “Femern project” includes a former fjord or lagoon, which was used both as an economic resource and as background for ritual activities in the Neolithic. The wetland conditions give excellent preservation conditions for organic material. A yet unsolved issue, however, is the question of reservoir effects. The local reservoir effect needs to be known for accurate radiocarbon (14C) dating of samples with possible aquatic carbon sources, such as human bones or food residues on pottery. Therefore, this paper attempts to calculate the local reservoir effect for the study area. I will discuss the possibilities and limitations when analyzing 14C dates from a rescue excavation. When applying the estimated reservoir corrections to a hoard of jaws and other bones, an interesting change in ritual activity at ca. 4000 cal BC can be observed. Furthermore, I examined 14C dates on bulk organic sediment and will discuss their implications for building chronologies and for reconstructing the environment of the Stone Age fjord. Finally, I will discuss the pitfalls and uncertainties associated with 14C dates for sea level reconstruction.