Nanoparticles (NPs) have emerged as ubiquitous contaminants in aquatic environments due to their extensive industrial, biomedical, and agricultural applications. Their small size, high surface reactivity, and potential for toxic ion release confer upon these particles a unique capacity to interact with aquatic biota, particularly planktonic communities, which form the base of aquatic food webs. This review compiles and analyzes recent ecotoxicological findings on the effects of metallic (Ag, ZnO, TiO₂, Cu, Fe₃O₄), polymeric, and composite nanoparticles on zooplankton and phytoplankton, with emphasis on physiological, biochemical, and population-level responses. Evidence indicates that NPs can induce oxidative stress, membrane damage, growth inhibition, reproductive impairment, and metabolic disruptions in species such as Daphnia magna, Ceriodaphnia silvestrii, and Chlorella vulgaris. Ionic dissolution (e.g., Ag⁺, Zn²⁺) and reactive oxygen species (ROS) generation have been identified as primary toxicity pathways, although surface interactions and protein corona formation also modulate their bioavailability and toxicity. Sublethal and chronic exposures often disrupt planktonic community composition and productivity, with potential cascading effects on higher trophic levels and ecosystem stability. Despite advances, significant knowledge gaps persist regarding long-term ecological consequences, toxicity of mixtures with other pollutants, and NP behavior under environmentally realistic conditions. Future research should integrate mechanistic toxicology, nanoinformatics, and ecological modeling to predict environmental fate and impacts of NPs. The synthesis of green nanoparticles and implementation of standardized testing protocols are crucial for risk mitigation and guiding sustainable nanotechnology practices. By elucidating the complex interactions between NPs and planktonic organisms, this study contributes to a broader understanding of nanoparticle-induced perturbations in aquatic ecosystems and their implications for environmental health.