Baltic Sea oxygen levels at '1,500-year low due to human activity'

Nutrient run-off from agriculture and urban sewage are likely to be to blame, scientists say

The coastal waters of the Baltic have been starved of oxygen to a level unseen in at least 1,500 years largely as a result of modern human activity, scientists say. Nutrient run-off from agriculture and urban sewage are thought to be to blame.

"Dead zones" - areas of sea, typically near the bottom, with a dearth of oxygen - are caused by a rise in nutrients in the water that boosts the growth of algae. When these organisms die and sink to the seafloor, bacteria set to work decomposing them, using up oxygen in the process.