Algae, which are a wide group of photosynthetic organisms that range from microscopic microalgae to larger seaweeds, have been recognized for their environmental advantages for a long time. These benefits include carbon sequestration and nutrient cycling. As a result of their capacity to rapidly proliferate and absorb heavy metals, they have recently emerged as powerful agents for the production of nanoparticles. This chapter examines the green synthesis of nanoparticles, specifically through methods that involve algae. These approaches provide a sustainable alternative to the conventional chemical and physical synthesis techniques currently in use worldwide. Algae-based nanoparticle synthesis is an environmentally friendly, cost-effective process that utilizes the natural capabilities of algae to generate metal nanoparticles such as silver, gold, and copper. Conventional methods, on the other hand, produce hazardous byproducts and require a significant amount of energy. Algae-mediated synthesis for environmental applications, such as wastewater treatment, has received insufficient research even though it holds a great deal of potential. The chapter emphasizes the necessity of conducting additional research into the mechanics of algal nanoparticle synthesis as well as the development of alternative, environmentally friendly production methods. In addition, it addresses case studies, obstacles, and potential paths for the advancement of phyco-nanotechnology for environment sustainability.