High levels of mercury contamination have entered the aquatic ecosystem primarily through:
 a
Medications like vaccines which contain mercury and subsequently enter the drainage systems through human waste.
 b
Emissions from coal burning power plants which then rain down on waterways.
 c
Merurcury solutions which are used in plastic production and then disposed of through waste water.
 d
Paper productions which uses mercury in a bleaching process to whiten the paper.