Carp are greyish to bronze in colour and have two fleshy barbels projecting downwards on either side of the mouth.  The number of scales varies greatly.  The most common type of carp, the king carp, has a full set of scales.  The mirror carp has a single row of large scales along the sides.  The leather carp have no scales at all.  

Carp originated in the River Danube, and were introduced to Britain by the Romans as a source of food.  They are hardy fish and can tolerate a wide range of conditions.  However, they do best in large bodies of fresh water with slow flowing or still water, with soft muddy sediments.

Carp are omnivorous; they feed on aquatic crustaceans, insects, worms, aquatic plants, algae and seeds.  They grub around in the sediment and strain food from the mud, which can cause problems because this action uproots submerged vegetation and increases the cloudiness of the water.  This can have negative effects on native wildlife.  

More information and images of common carp are available on the Arkive website.
http://www.arkive.org/species/ARK/fish/Cyprinus_carpio/