Jinhae Bay is the first of Koreas two major dead zones, hypoxia was first reported in Jinhae Bay in September of 1974. In 2011, a joint study was done to observe and record causes, effects, and what can be done about Koreas hypoxic zones. It was discovered that Jinhae Bay exhibits a seasonal dead zone from early June to late September. This dead zone is caused by "domestic and land use waste and thermal stratification". Jinhae Bay experiences hypoxia largely at the bottom of its bay. The ratios of Phosphorous to Nitrogen is imbalanced at the bottom, where its otherwise balanced at the top, with the exception of early June to late September where the Bay is experiencing eutrophication as a whole. The effects of Jinhae Bay's hypoxia is seen in the marine system surrounding Korea, with a loss of biological diversity, particularly of the calcareous shelled organisms.