name of a Chinese river, snivel
泗 centers on liquid discharge from the face: sniveling or weeping. The river name is a specific geographic application of that water-related idea.
泗 combines 氵 (water) with 四, which likely contributes the sound. The character originally referred to a river and later extended to nasal mucus or tears.
Water 氵 beside the number four 四: imagine four streams of tears or mucus flowing down a face.
For シ, picture a sniffling child saying 'shee' as they wipe their nose: 'shee' cues シ while the water radical suggests the snivel.