Safety tests on Norfolk and Cambridgeshire canal tip
An investigation is under way to check if an abandoned canal on the Norfolk and Cambridgeshire border, used for many years as a tip, is contaminated.
Fenland and West Norfolk councils have sent more than 1,000 warning letters about precautions during the tests.
Families living along the five-mile line of the Wisbech canal are asked to wear gloves when gardening and to prevent children playing in the soil.
In 1961 the canal was used for landfill but tipping stopped in the 1970s.
The two councils are checking if anything put in the old canal between Wisbech and Outwell at the time could be harmful if it gets into gardens, houses or water supplies.
Until the survey is finished residents have been asked to take precautions.