Possible Clues:

• A watercourse, and the way it can absorb an artist
• Not, by the sound of it, round the bend in the narrow sense
• Birds crossing a river heading north for sea channel
• By the sound of it, not a crooked one of the 6 down
• Channel's second distinguished characteristic
• Getting passage immediately, you say
• Narrow sort of traits (6)
• Artist's fanciful representation of a watercourse
• Difficult position of Gibraltar, for example
• Sibelius's first characteristic passage