Balekambang Lake, one of the lakes on the Dieng Plateau, is a lake that has banks of organosol soil that continue to grow, causing lake size shrinkage. The identical phenomenon occurs in several other lakes on the Dieng Plateau, making it a threat to the existence of the lakes and a concern for the ecosystem within them. Diatoms are microalgae (Bacillariophyta) often used as indicators due to their sensitivity to environmental changes. The inorganic nature of their silica structure makes them well preserved in the depth of sediment. This study was conducted to determine the diatom community structure in the sediment stratigraphy of Balekambang Lake banks. A total of 250 cm of sediment was sampled vertically using a dissection corer. Each 10 cm of soil in the sample was digested using 10% H2O2 and 10% HCl and then prepared using the Battarbee method. The sample was observed under a 1,000-magnification student microscope. A total of 86 diatom species from 31 different genera were found in Balekambang Lake; Diversity and the diversity and evenness index values of the diatom community were relatively moderate to high, indicating good ecosystem stability. A high abundance of eutrophic indicating diatoms such as Cylotella meneghiniana, Nitzchia palea, Navicula cryptocephala, and Staurosira construens were found across sediment stratigraphy. Domination of Staurosira pinnata, an alkaline tolerant species, was found at a depth of 230 cm, indicating unstable of the ecosystem caused by ecological variability such as pH fluctuations. The indicated high level of nutrients in Balekambang Lake that is contributing to the ongoing eutrophication could result from Dieng’s land use for settlement and agriculture that produce organic pollution to the lake.