Context: In a recent event, Russia alleged that the British warship had breached its territorial waters in Black Sea which Britain and most of the world say belong to Ukraine.

• Russia seized and annexed the Crimea peninsula from Ukraine in 2014 and considers areas around its coast to be Russian waters.

About Black sea

• Black Sea is a marginal sea of the Atlantic Ocean. It is located between Eastern Europe and Western Asia 
• Border countries: Black Sea is bordered by six countries – Romania and Bulgaria to the west; Ukraine, Russia and Georgia to the north and east and Turkey to the south. 

Connecting water bodies

• The Black Sea ultimately drains into the Mediterranean Sea via the Turkish Straits and the Aegean Sea.  
• The Bosporus Strait connects it to the small Sea of Marmara which in turn is connected to the Aegean Sea via the Strait of the Dardanelles.  
• To the north, the Black Sea is connected to the Sea of Azov by the Kerch Strait. 

Meromictic Basin

• The Black Sea is the world’s largest body of water with a meromictic basin. 
• A meromictic lake has layers of water that do not intermix. The deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. 
• As a result, over 90% of the deeper Black Sea volume is anoxic water. Anoxic waters are areas of sea water, fresh water or groundwater that are depleted of dissolved oxygen. 
• Hence, anoxic layer is responsible for the preservation of ancient shipwrecks which have been found in the Black Sea.