'algae-poor' is a modern English compound formed from 'algae' + 'poor'. 'algae' originates from Medieval Latin, specifically the word 'alga', where 'alga' meant 'seaweed'. 'poor' originates from Old French, specifically the word 'povre' (from Latin 'pauper'), where 'pauper' meant 'poor'.

'algae' passed into English usage from Medieval/Neo-Latin 'alga' (itself from Ancient Greek 'άλγη'/'αλγη' relating to seaweed) and is used in Modern English as 'algae' for the organisms; 'poor' came into English via Old French 'povre' (Middle English 'povere') and eventually became the modern English adjective 'poor'. The compound 'algae-poor' is a recent descriptive formation in scientific and environmental contexts.

The compound has kept a literal compositional meaning: initially formed to mean 'having little or no algae', and it continues to be used in that direct, descriptive sense in contemporary usage.