Aquatic habitats with moderate amounts of vegetation provide the optimal environment for many aquatic animals especially the fish diversity. High density of plants would hamper the fish growth, health and the water quality. Aquatic weeds pose significant threat to water bodies. In India, several irrigation and hydroelectric schemes acutely suffers due to the massive outbreak of aquatic weeds. There are about 140 aquatic weeds in India, in that Eichhornia crassipes, Ipomoea aquatica, Typha angustata, Ceratophyllum demersum, Salvinia molesta, Nelumbo nucifera, Alternanthera philoxeroides, Hydrilla verticillata, Vallisneria spiralis,, Chara spp., Nitelia spp., Potamogeton spp., are of great concern in terms of outbreak and its impact on the water quality. For example, the water hyacinth ((Eichhornia crassipes) mats clog waterways, making fishing and all other water activities, impossible. Water flow through water hyacinth mats is greatly diminished. An acre of water hyacinth can weigh more than 200 tons; infestations can be in many acres; mats may double their size in as little as 6-18 days. Water hyacinth mats degrade water quality by blocking the air-water interface and greatly reducing oxygen levels in the water, eliminating underwater animals, it also greatly reduces biological diversity and eliminates native submerged plants by blocking sunlight, alter emerged plant communities by pushing away and crushing them. Millions of dollars a year used to spent on water hyacinth control in many countries. In the present attempt, the grass carp (Ctenopharyngodon idella) has been used as a biological control agent to control or manage the outbreak of the aquatic weeds like water hyacinth, Hydrilla and Giant duck weed to improve the water quality is discussed with field level case studies.