Since the early 1980s, more or less widespread hypoxia has been observed nearly every autumn in Danish coastal waters. Water exchange in Skagerrak is limited and hypoxic conditions in deep basin are common, because water renewal, which takes place only once a year, causes stagnation period with hypoxia in the winter. Several fjords on the Swedish and Norwegian Skagerrak coast have shown negative trends in dissolved oxygen content, and some of them lack benthic fauna in the deeper parts for several months or more. Swedish fjords of the Skagerrak coast experience hypoxia and anoxia for most of the year. In Norway, for instance in Oslofjord, the benthic fauna has suffered from mortality and behavioral changes. Since around 1960-70s, dissolved oxygen content has reclined in Oslofjord. Improvements in sewage treatment and discharge practices have been made.