'shallow-water' is a compound formed from the adjective 'shallow' and the noun 'water'. 'Shallow' originates from Old English (Anglo-Saxon) 'sceald' / 'sceald(e)' meaning 'not deep' or 'having little depth', and 'water' originates from Old English 'wæter', from Proto-Germanic '*watōr' meaning 'water'.

'shallow' changed from Old English forms like 'sceald' into Middle English 'shalow' and eventually the modern English 'shallow'. 'water' evolved from Old English 'wæter' to Middle English 'water' and then to modern 'water'. The modern compound 'shallow water' has been used in English for centuries to describe water of little depth.

Initially the separate words referred to the qualities 'not deep' and 'water'; combined they have consistently meant 'water of little depth', and that core meaning has remained stable into modern usage, with extended adjectival uses (e.g., 'shallow-water species').