Traders in Wallingford are bracing themselves for the disruption when High Street closes for two weeks on August 28.
Following complaints about cellars flooding, Oxfordshire County Council is to close part of the street, from the Lamb crossroads as far as Bedz at No 33, for drain repairs.
The road will be closed from August 28 to September 1, and from September 3 to 11 inclusive.
Highways engineer Gordon Hunt said he hoped the work could be finished in less than two weeks.
He added: "We will do all we can to help deal with any problems residents or businesses have with deliveries."
Town clerk Andrew Rogers predicted disruption, but said it was necessary to "bite the bullet" and get Wallingford's ailing sewerage network improved.
However, traders fear sales could be hit and claim the timing is far from ideal.
Deborah Balchin, who owns Occasions Unlimited, said: "As per usual, it's small businesses that must pay the price. Why don't they do this work in February instead of right after the August bank holiday when everyone has just been paid? There will still be a lot of tourists in Wallingford at the end of August."
Peter Waters, owner of Waters Violins, said: "The worry is that it will deter customers from coming into the town centre."
Diverted traffic will be able to use Thames Street, St George's Road, and the ring road.
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