A collapsing garden could cause problems for an annual rowing event known as the Henley of the North.
The Durham Regatta is due take place on the River Wear on 8-9 June.
However, a section of the St Oswald's vicarage garden, including a large tree, has slid down the bank into the river just below Kingsgate Bridge.
Organisers said they were hopeful the obstruction would be removed in time for the regatta, which attracts top rowers from the UK and abroad.
Charly Curtis, head of the Durham Regatta race committee, said: "There is no way with the tree as it is that you could safely get two racing eights side-by-side through this part of the river.
"Steering through Elvet bridge and round the corner is difficult enough without any obstructions. Hopefully it will all be sorted out in the next few weeks and we can run a safe and competitive regatta."
The riverside footpath has been closed while Durham County Council carries out stabilisation work, and the river itself is being dredged to remove flood debris.