Gregarious behaviour and congregation on holding areas.
First of all, they don't move around much. Very often we see groupings (which can be very large) around what are called holding areas. In dams this corresponds to rocky screes, fields of submerged stumps, or deep, congested edges. They descend into the water layer to find a temperature less cold than at the surface, the thermal boundary between the very cold surface water layer and the warmer deep zone. This limit is called thermocline, and to reach it the carps do not hesitate to gather at a depth of 10 or 15 meters in a reservoir. In rivers they will occupy places sheltered from strong currents, protected by tree trunks or any other natural or artificial structure breaking the main current. This provides them with security and limits their energy expenditure, so precious in this season.