The project will focus on the role of an invertebrate omnivore Mysis relicta in mercury and POPs bioaccumulation in Lake Mjøsa. Mysis is in the lake a key species linking by its vertical migration behavior benthic and pelagic food webs and likely transpor ting environmental pollutants from sediments to fish. This study will test a hypothesis recently developed by a related project ToxLake, that difference in concentration of contaminants in Mysis are influenced by different vertical migration behavior of M ysis in shallow and deep parts of the lake.