Young Avestan nāuuiia-, Old Persian nāviyā, Sanskrit nāvyà-, all descending from Indo-Iranian *nāu̯ii̯a-, are usually glossed by ‘passable (only) by boat, not to be crossed without the help of a boat’. A closer examination of the contexts they occur in reveals that the meaning ‘streaming, raging’ is much more appropriate. In consequence, *nāu̯ii̯a- can not be a secondary derivative of Indo-Iranian *nāu̯- ‘ship, boat’, which is improbable for other reasons as well. It is suggested that *nāu̯ii̯a- rather represents a primary formation derived from the Indo-Iranian root *nāu̯- ‘to flow’.