<p>The diagnosis of drowning represents a considerable challenge in forensic practice. Typically, it is made by excluding other potential causes of death while concurrently identifying key signs of drowning. However, in cases with a prolonged postmortem interval, these characteristic signs are often absent. To support drowning diagnoses, various supplementary methods have been introduced over time, prominently including qualitative and quantitative diatom tests. One such approach involves comparing diatom concentrations in the drowning medium (immersion water) and in the lung tissue to determine lung-to-drowning medium (L/D) ratios. L/D-ratios above 2 are thereby seen as safe indicators of drowning, as higher diatom concentrations in the lungs than in the drowning medium can only be explained by active water aspiration. Previous studies typically investigated diatom concentrations in the tip of the lung’s left superior lobe, as this region is thought to generally experience the lowest physiological pressure. However, no experimental data have yet confirmed the relevance of this in drowning incidents. It is also still unclear how diatoms are distributed within the lung during aspiration and how L/D-ratios could vary if samples from other lung regions are used for L/D-ratio calculations. To address these uncertainties, we conducted a study assessing diatom concentrations across seven positions from all pulmonary lobes in 25 drowning cases. Our aim was to identify the lung regions with the lowest probability of diatom uptake, thereby maximizing the reliability of L/D-ratios as a forensic tool. Our findings show that the left superior lung lobe is indeed the site of the lowest diatom accumulation and thus optimal for L/D-ratio related drowning diagnosis. Nonetheless, due to the higher sensitivity for diatom uptake, inclusion of other lung positions may also be recommended to strengthen diagnostic accuracy, especially in cases with generally low L/D-ratios.</p>