Police are treating man-made bike jumps on protected scientific land in Kesgrave as criminal damage.
Officers from Suffolk police are looking into the jumps, constructed on land near Sinks Pit, off Hall Road.
The land is protected as a Site of Special Scientific Interest, with the ground having been dug up to create the jumps said to have been built some 6ft high.
Police believe the track was created over a three week period, and said they have received reports of men in their 30s being seen on site.
Those with any information regarding who was responsible, or who have seen any suspicious activity in the area, are asked to contact police on 101 and quote crime number 37/25724/21
Alternatively, information can also be given anonymously to charity Crimestoppers on 0800 555111.
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