In this paper, we have studied the rapid synthesis and antimicrobial activity of silver nanoparticles synthesized using extract of Eichornia crassipes (Water Hyacinth) which is considered as one of the most notorious aquatic weeds present all over the world. The synthesized nanoparticles exhibited absorption maximum at 420 nm which is a characteristic feature of Surface Plasmon Resonance (SPR) peak for silver nanoparticles. The silver nanoparticles were characterized with Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) and found the size ranges from 10 to 50 nm. Further Fourier Transformation Infrared Spectrum (FTIR) revealed that the phenolic groups present in the plant extract were responsible for the reduction of silver nitrate into silver nanoparticles and stabilization of formed silver nanoparticles. Finally antibacterial activities of the silver nanoparticles were checked against Bacillus subtilis, Pseudomonas fluorescens and Klebsiela pneumonia and significant zones of inhibition were found.