Research into the processes of organic matter redistribution and transformation and the distribution of iron forms in the lake sediment column are of high relevance. Data from longterm monitoring in Kondopoga Bay provide insights into the processes that influence the formation of bottom sediments. The research results confirm that the incoming organic matter is of dual origin – autochthonous, due to significantly high productivity in part of the bay, and allochthonous, terrigenous matter of humic nature. Entering the bay, it settles to the bottom. The organic matter content of the sediments is related to their particle size distribution and iron content. A correlation between these indicators was revealed.