Sledge hammers, gas cylinders and engine parts have been found in bin collections.
Amey is appealing to residents to take unwanted metal items to the Wisbech tip rather than throwing them out into the black bin collections.
Several tonnes of large metal items have been found at the firm’s mechanical biological treatment plant, which could cause damage.
Plant manager Alex Fishlock said: “We have metal items such as large weights, dumbbells, sheeting, fire extinguishers and gas cylinders blocking the machinery.
“You can see cuts in the metal surface where the bag splitter teeth have cut, which can cause the teeth to break.
“Gas cylinders and fire extinguishers are particularly dangerous because they can explode.”