The Bay of Somme is a large estuary characterized by strong marine influence, low freshwater input and strong hydrodynamical processes. The first effects of eutrophication were observed in the beginning of the 1980s. The estuarine fauna is well adapted to permanent stress by tide and freshwater input. Episodic hypoxia has caused mass mortality of the benthos with multi-year recovery and collapse of cockle fishery.

In addition to the eutrophication, the drivers for the hypoxia in the Bay of Somme are exceptional weather conditions (high temperatures, eastern winds) and neap tides restricting mixing of water, bloom period with high oxygen consumption rates and degradation of phytoplankton, and the presence of shallow, oxygen-poor pools colonized by high densities of macrofauna.