History of the North Sea the North Sea though they saw little action. The Austro-Prussian War (1866) resulted in Prussia's gaining full control of the Kiel Canal, allowing their Baltic ports access to the North Sea. France declared war on Prussia 19 July 1870 which initiated the Franco-Prussian War (1870–1871). The French Navy was, at the time far larger and superior to the North German Federal Navy, the Navy of the North German Confederation. Though the French did take a number of merchant ships bound to and from North Germany, shortages of manpower and coal, as well as conflicting orders, made the attempted blockade of
Baltic Sea hypoxia can occur. the total area of bottom covered with hypoxic waters with oxygen concentrations less than 2 mg/l in the Baltic Sea has averaged 49,000 km over the last 40 years. In the Baltic Sea, the input of salt water from the North Sea through the Danish Straits is important in determining the area of hypoxia each year. Denser, saltier water comes into the Baltic Sea and flows along the bottom. Although large salt water inputs help to renew the bottom waters and increase oxygen concentrations, the new oxygen added with the salt water inflow is rapidly used to decompose