What does Blake mean?
From two Old English words that fell together in Middle English: 'blaec' meaning 'black, dark' and 'blac' meaning 'pale, fair'. This produces a true opposite-meaning dispute, and for any given bearer it is usually impossible to tell which sense was meant.
What does River mean?
An English nature name taken directly from the word 'river' (ultimately from Latin riparia, riparius 'of the riverbank').