Artist designed channel (6)
I believe the answer is:
strait
'channel' is the definition.
(strait is a kind of channel)
'artist designed' is the wordplay.
'designed' indicates anagramming the letters (designed with the letters).
'artist' is an anagram of 'STRAIT'.
(Other definitions for strait that I've seen before include "Narrow sorts of traits" , "Hardship - narrow passage of water" , "Narrow passage joining two large areas of water" , "Narrow stretch of sea" , "Narrow or difficult" .)