EPA diver Mel Parsons at the Tippo Bayou sampling station in the Mississippi Delta near Philipp, MS in August, 2011.
In what looks more like pea soup, this diver was helping to collect 'Sediment Oxygen Demand' information. Sediment oxygen demand refers to how much oxygen is being used by organisms and plants in the sediment. Oxygen within the sediment underwater normally accounts for 40-70% of the oxygen used within a body of water.
EPA uses these measurements to better understand the overall health of bodies of water. It provides precise environmental information for 'total maximum daily load' (TMDL) studies which help to inform water pollution regulations.