<p>Decomposition studies are pivotal for forensic science, offering insights into postmortem events. While decomposition dynamics in static environments are well-documented, transitions between subaerial and aquatic settings remain underexplored, particularly in diverse ecological regions. Decomposition rates were investigated in juvenile piglets subjected to subaerial-to-freshwater aquatic and freshwater aquatic-to-subaerial transitions. Twelve piglets were used in total: five in each experimental group and two controls, each exposed exclusively to either subaerial or aquatic conditions. Decomposition progression was quantified using Adjusted Total Body Scores and Total Aquatic Decomposition Scores, which were standardized for cross-environment comparison. Accumulated Degree Days were calculated to account for thermal input. The subaerial-to-aquatic transitions exhibited delayed decomposition initially, followed by rapid tissue breakdown post-submersion, often leading to near-complete skeletonization. In contrast, aquatic-to-subaerial transitions displayed rapid decomposition during submersion, followed by reduced activity and partial or complete mummification after environmental change. These shifts were reflected in scoring results but also revealed morphological changes not accounted for in current scoring systems. Transitions between environments significantly alter decomposition rates and patterns. Existing scoring systems proved limited in accounting for these shifts, particularly in cases of mummification. Findings from this study highlight the need for a novel scoring framework tailored to fluctuating environments and calls for further research into decomposition morphology specific to environmental transitions.</p>