Without looking it up, what's your guess how to pronounce "slough"?
Let's use words starting with "t" as a starting point. Does the ough in slough sound like the ough in thorough, thought, through, tough, or trough?
This Carlinesque reflection was inspired when my wife and I came across and differently mispronounced this word unfamiliar to both of us. Crossword and scrabble geeks might scoff at our ignorance but only those from that nerdy group who can come up with a better pun than the title of this post are allowed to gloat and take a bough. Just the same, let's all be kind to people learning English, OK?