Possible Clues:

• This may have the doctor on edge, but he'll get to the bottom of it
• Channel maintenance machine
• Clear river bottom
• Clean out from river bottom or harbour
• Sort of collector to show irritability when faced with debtor
• Clean bed with empty drawer by the side
• (Of harbour or river) make deeper
• Perhaps Stel slackens like this
• River cleaner
• Scour (riverbed); sprinkle with sugar