Dirt sea spread across both sides of bay, perhaps (7)
I believe the answer is:
astride
'across both sides of bay perhaps' is the definition.
I can't judge whether this definition defines the answer.
'dirt sea spread' is the wordplay.
'spread' indicates an anagram.
'dirt'+'sea'='dirtsea'
'dirtsea' anagrammed gives 'ASTRIDE'.
Can you help me to learn more?
(Other definitions for astride that I've seen before include "on horseback" , "With one leg on either side, as sitting on horse" , "It dares to be with legs wider apart" , "With feet apart" , "On the back of" .)