<p>Because meromictic lakes lack bioturbation, their sediment layers are preserved at depth and contain a wealth of environmental information indicating changes over time. This study examined phosphorus (P) fractions and ecological risks in sediment cores taken from Lake Köyceğiz (LK), the first meromictic lake identified in Türkiye. Sediment core samples were taken from six different stations at a depth of 20&#xa0;cm in four different seasons and were divided into 2&#xa0;cm sections for analysis. The trophic status of the water in LK was variable, but generally eutrophic and hypertrophic. Due to the dominance of AP in the sediment, it was determined that the contribution of endogenous P to the ecological risk in the lake is low, while exogenous P is the primary factor affecting ecological risks. Trend analysis also revealed that the P load in the sediment has increased over time due to the increasing population and anthropogenic activities following the region's transformation into a major tourism area. It was emphasized that some meromictic lakes may lose their stratification properties due to climate change, leading to changes in water and sediment structure. Therefore, it is stated that ecological risk studies should be continued to ensure the sustainable protection of meromictic lakes. Therefore, this study is expected to be an important reference for future limnological studies in meromictic lakes and LK.</p>