The most common and most likely answer to this crossword clue is the 6 letter word CANALS
I've seen this crossword clue in The Daily Telegraph
C
A
N
A
L
S
Buddy explains!
The straight part
We know that "waterways" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waterways = canals.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CANALS mean?
CANALS noun- An artificial waterway or artificially improved river used for travel, shipping, or irrigation.
- A tubular channel within the body.
- One of the faint, hazy markings resembling straight lines on early telescopic images of the surface of Mars.
- To dig an artificial waterway in or to (a place), especially for drainage
- To travel along a canal by boat