Lake Erhai and its adjacent areas at one time constitute one complete source-to-sink (S2S) system. According to analyses of modern S2Ss, however, the S2S of Lake Erhai Basin can be divided into three subsystems — western (S2S-W), eastern (S2S-E), and northern (S2S-N). Among these three subsystems, significant differences have been found to exist in bedrock lithology (source area) and sedimentary bodies (sink area). The bedrocks (source area) of S2S-E consist mainly of carbonate rocks, and sediments are transported by small rivers and deposited on the eastern bank of the lake, forming small () alluvial fans (sink area). Bedrocks of S2S-W involve metamorphic rocks and a few granitic and carbonate rocks. Sediments are transported by extensive streams (Cangshan 18 streams) and deposited along the western bank of the lake, forming a large () sediment belt. In S2S-N (axial source), bedrocks are composed mainly of the clastic rocks. Sediments are transported by large rivers (the Miju and Lushi Rivers) and are deposited on the northern bank of the lake, forming a large delta (). Studies of the modern S2S reveal that different S2Ss can exist in the same basin (sag) and that these S2Ss are likely to differ significantly in catchment area, sedimentary body area, sedimentation response, etc., because of controlling factors such as bedrock lithology, tectonic activity, paleomorphology, basin boundaries, and transport channel, among others. Therefore, more attention should be paid to the distinguishing characteristics of S2Ss in further study of the ancient S2S systems.