Microbial public goods, including siderophores, heme, and catalases, underpin cooperative interactions in aquatic environments. These extracellular compounds enable resource acquisition, stress mitigation, and metabolic cross-feeding, helping aquatic microbial communities cope with environmental stress and sustain their ecological roles. Because public goods are freely available to surrounding cells, their production involves balancing individual cost and community benefit, generating conflict between cooperation and cheating. External cues such as nutrient limitation, salinity shifts, and oxidative stress modulate the production and utilization of microbial public goods. Aquatic systems are physically homogeneous and dilute, fostering metabolic interdependence by increasing reliance on externally available compounds and shaping cooperation through dependency rather than autonomy. In parallel, genomic traits such as gene loss or streamlining in oligotrophic aquatic taxa further reinforce this cooperative mode. Many aquatic microbes have lost the full genetic capacity to synthesize essential metabolites, including vitamins, siderophores, and antioxidants, making them dependent on extracellular metabolites provided by other community members. In such water environments, the production and accessibility of public goods become central to survival, fostering cross-feeding and collective stress responses. This shared resource dependence reinforces cooperation and drives community organization and functional interdependence, underscoring the ecological and evolutionary importance of public goods in shaping aquatic microbial ecosystems.