The Teesdale Wynch Bridge on the way to High Force will be closed for eight weeks, forcing ramblers to find an alternative route.
The historic Teesdale bridge, which is near Low Force waterfall and forms part of the route to High Force, has been closed to allow for urgent repair work.
The Wynch Bridge closure started on Monday October 7 and is expected to continue for about eight weeks.
Visitors to High and Low Force waterfalls may need to find an alternative route to see the landmarks following the Wynch Bridge temporary closure.
Brian Buckley, Durham County Council's strategic highways manager, said: "This structure is not only of historic importance, but it also provides a vital link across the River Tees, connecting walkers to the Pennine Way and High Force.
"We appreciate that for visitors walking between Bowlees Visitor Centre and High and Low Force waterfalls this may be an inconvenience. In the meantime, there are alternative paths and footbridges across the river.
"We thank everyone affected for their patience and understanding."
Following routine inspections, Durham County Council engineers identified that the Wynch Bridge in Teesdale required some urgent repair work. The almost 200-year-old Grade II listed Wynch Bridge will be closed to the public to allow the work to take place.
The scheme is expected to take eight weeks to complete and will see the replacement of the timber deck and suspension joints, as well as cleaning and re-painting of the iron works.
A signed diversion will be in place and visitors to the area can find out more information about the diversion from the Bowlees Visitors Centre, where diversion maps will be available.