Stable aqueous dispersions with high concentration of silver nanoparticles were synthesized by a facile and green synthetic route by treating silver ions with aqueous Citrus limon extract, used as a reducing and capping agent. The formation and growth of silver nanoparticles, prepared by this simple and convenient method, was monitored using UV-visible absorption spectroscopy. The effects of Ag concentration, Citrus limon extract concentration, in-situ and ex-situ pH variations upon NaOH addition on the structural, optical and plasmonic properties of the synthesized Ag nanoparticles were investigated. X-ray diffraction studies revealed the formation of Ag nanoparticles, whose morphology was studied using atomic force microscopy. UV-visible absorption studies revealed surface plasmon resonance (SPR) peak around 465 nm, confirming the presence of Ag nanoparticles. The SPR peak blue shifted along with significant enhancement in intensity with increase in Ag concentration and pH, due to the growth and increased aggregation of Ag nanoparticles. We have shown that addition of NaOH is a key to rapid biosynthesis of stable aqueous dispersions of high concentration of silver nanoparticles. This green synthetic route provides faster synthesis of silver nanoparticles with improved colloidal stability, which can be used in foods, cosmetics and biomedical applications.