This radar Envisat image features Russia's Volga Delta and the Caspian Sea. The Volga River (dark) rises northwest of Moscow and extends southward some 3700 km through the whole central part of the country where it pours into the Caspian, forming a delta of about 800 smaller waterways.
The Volga Delta is considered one of the world's most dynamic deltas because of its remarkably complicated hydrographic network. Its winding channels, marshes and wetlands provide a comfortable home to a rich variety of fauna and flora species.
More than 70 000 fish species inhabit its waters, making it one of the best places to fish in Russia and earning it the nickname 'the 24-hour bite' among locals. Since the area provides habitat for many migrating birds, it is designated as a Wetland of International Importance.
Among the flora species, its most renowned is the lotus, or Caspian rose. They usually bloom in July and last through September. In mid-July this year, tourists flocked to the delta to see the flowers blossom in what is believed to be the largest field of lotus on the planet: 3 km by 15 km.
Covering an area more than 380 000 sq km, the Caspian Sea is larger than Japan. The northern part of the sea (seen here) is the most shallow, averaging about 10 m deep. Vast oil and gas reserves are located here, making it the subject of major exploration and exploitation efforts.
Since the sea has no outlet, many unique animals and plants have been preserved; it is home to 85% of the world's stock of sturgeon and is the source of 90% of all black caviar.
The Russian city of Astrakhan, on the Volga Delta about 100 km from the sea (visible in white just above the triangular delta), remains at the centre of the caviar trade.
This image was created by combining three Envisat radar acquisitions (8 April, 13 May and 17 June) over the same area. The colours result from changes in the surface that occurred between acquisitions.