Relating to or characteristic of rivers; of or pertaining to fluvial processes and river systems.
From Latin fluvius (river) + -atic (suffix forming adjectives). The -atic suffix is related to -atic in words like aquatic and hepatatic, all deriving from Latin roots.
Languages love synonyms, and fluviatic is basically a fancier, more technical sibling to fluvial—scientists sometimes use both interchangeably to add variety to their writing.
Complete word intelligence in one call. Free tier — 50 lookups/day.