Mercury is highly noxious heavy metal. It exists in three forms: Elemental, organic, and inorganic. All forms of mercury have proven to induce toxic impacts on the living beings. It has ability to accumulate in the different tissues of the body and magnifies its concentration from lower to higher trophic level. Mercury has been introduced to aquatic body mostly via different anthropogenic activity. Thermal power plants which uses coal as the main fuel is identified as primary source of mercury contamination in air. From air it gets deposited on land surface and finally washed to water body. The aquatic plants and animals are the process through which it enters the food web. In Aquatic ecosystem, organisms get exposed easily and consume mercury that deposits in their gills, liver, kidney or gonadal tissues. Hg has its potential impacts at both either acute or chronic exposure level. The severity of toxicants depends upon duration of exposure, method of exposure and amount of dose. The present study gives an insight of toxic impacts of mercury in aquatic ecosystem.