Cyanobacterial blooms can negatively affect aquatic ecosystems by altering their trophic structure and functionality. Monitoring physical-chemical parameters is crucial for understanding these blooms, and dissolved organic matter (DOM) plays a key role in both abiotic and biotic processes. However, the impact of DOM on cyanobacterial growth and phytoplankton community structure is not well-studied. This research explores how different DOM types affect the growth of potentially harmful cyanobacteria and the overall phytoplankton community. The study examines the effects of four natural freshwater DOMs from Australian water bodies on the growth of cyanobacteria Chrysosporum ovalisporum. The DOMs, with varying characteristics like aromaticity, molecular weight, and the presence of proteins, humic, and fulvic acids, were tested at three concentrations (0, 2, 10, and 20 mg L⁻¹) over a 14-day period. Additionally, phytoplankton communities from Lake Hume, Australia, were exposed to three DOM treatments (control, and 2 mg-C L⁻¹ of more labile and recalcitrant DOM) to assess the broader community impact. Results showed that all DOM treatments initially stimulated C. ovalisporum growth, regardless of concentration or DOM characteristics. However, after two weeks, some DOM types, particularly those rich in humic-like substances, high aromaticity, and large molecular weight compounds, inhibited growth, even at low concentrations. Conversely, DOM from autochthonous sources with higher protein-like content and lower molecular weight continued to support growth. Additionally, community composition varied significantly: DOM rich in humic substances suppressed C. ovalisporum while promoting diatom growth, while DOM with less aromatic, lower molecular weight proteins favored cyanobacterial proliferation. These findings highlight the complex role of DOM in shaping phytoplankton communities and emphasize the need for further study of DOM's ecological impact in freshwater ecosystems.