Twisted wire could be a danger to riverboats (4)
I believe the answer is:
weir
'be a danger to riverboats' is the definition.
I can't tell whether this definition defines the answer.
'twisted wire' is the wordplay.
'twisted' indicates an anagram.
'wire' anagrammed gives 'WEIR'.
'could' acts as a link.
Can you help me to learn more?
(Other definitions for weir that I've seen before include "Small dam built across river to regulate flow" , "Barrier" , "Low dam across a river" , "Dam on a stream to control water level or flow" , "fish may be trapped in this enclosure" .)