Sisyphean
Context : Attempting to fish out this drifting morass of trash using conventional methods-vessels, more nets-would a Sisyphean task. Source : The Atlantic ; February 4, 2019; p 42, The Widening Gyre . Sisyphean : [ˌsisəˈfēən], ADJECTIVE (of a task) such that it can never be completed. Endlessly laborious or futile. Sisyphus: a legendary king of Corinth condemned eternally to repeatedly roll a heavy rock up a hill in Hades only to have it roll down again as it nears the top.