The most common and most likely answer to this crossword clue is the 8 letter word OUTHOUSE
I've seen this crossword clue in Financial Times
O
U
T
H
O
U
S
E
More clues leading to the result OUTHOUSE
- Where to store stuff you formerly dumped in river
- Barn you once used to block Yorkshire runner
- Zero exercise with you getting stuck in that shed
- Toilet possibly? Previously you needed to go in river
- Shed you once installed in river
- Construction you once put in river
- Shed you found flooded by river
- Toilet historically you found in a river
- Shed, say, you once found fringed by river
- Shed, old ramshackle hut by river
Buddy explains!

The straight part
We know that "shed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shed = outhouse.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 OUTHOUSE mean?
OUTHOUSE noun- An outbuilding—typically permanent—containing a toilet or seat over a cesspit.
- Any outbuilding: any small structure located apart from a main building.