Work to repair one of Cumbria's most popular walking and cycling paths after the floods could take up to two years to complete, the National Park Authority has said.
Two bridges have been washed away between Keswick and Threlkeld and a third is in imminent danger of collapsing.
The former railway line forms part of the C2C cycle route which is used by thousands of people each year. A diversion has now been put into place.
The bridges had stood since the railway line was first built in the 1860s:
One has been pushed across the river by the weight of the flood waters
Another has been smashed completely with only a small amount of debris showing
A third is still standing, but has been seriously damaged. It has had to be closed until it is made safe
Cath Johnson, an Area Ranger with the Lake District National Park, has said: "Although it looks perfectly ok, after Storm Desmond we soon realised that there was serious damage to the abutments, that is the structure that actually supports the bridge, and it is at serious risk of collapse.
"It could literally go at any time and we've set up a monitoring programme with staff and volunteers to inspect it on a regular basis."
As well as damage to the bridges, part of the path has disappeared into the water on one section of the four mile route.
The National Park Authority estimates all the work will take between 18 months and two years to complete and could cost up to £5 million.
One section, a stretch of boardwalk near Keswick, should re-open soon, but people are being asked to keep away from areas that are closed and dangerous.
Regular updates will be put onto the authority's website.