The cost of repairing the ancient bridge and surrounding pathways at Tarr Steps will run into thousands of pounds.
Somerset County Council and Exmoor National Park say the landmark on Exmoor has been affected by landslips, fallen trees and erosion from recent flooding.
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Pupils at Hayle Community School launched the pasty as part of a project they are undertaking.
After a dry end to the day, it will grow colder overnight with a light breeze.
It will turn chilly tonight with largely clear skies and light winds.