For determining the process of bacterial aggregation, glucose was added into water from Lake Baikal which had been stored for seven months. In the presence of a higher concentration of glucose, the abundance of single bacteria and aggregates were higher, but the biovolumes of both bacteria were similar. Theses results mean that both free-living and aggregated bacteria have similar maximum sizes and that aggregates are forming with available organic materials. With available organic materials, the biovolume of aggregates becomes larger.