External Water Exchange of Lakes as the Integral Indicator of Water Body Types

External water exchange of overflow lakes is presented as the integral indicator, defining the type of lake basin. Intensity of water replacement in the lake (K_w) determines many processes taking place in the lake and its drainage area. Simultaneously this process influences the runoff of the outflowing river. Among the processes in the lake, depending on K_w, transitory-accumulative possibilities, predominance of allochton and limnic processes, and the participation of K_w in forming trophic status are considered. Some examples of the dependence of the parameters of lake level distribution curves upon the K_w values are given. The problem of calculation of K_w for unexplored objects is also regarded. The text contains specific examples of the results of calculations and analysis.