Youngsters have been warned against risking their lives by leaping 30ft from a bridge into the River Ouse.
Tombstoning has claimed a number of lives across the UK
The warning comes from the Environment Agency after footage of youngsters "tombstoning" in St Neots was filmed and put on the YouTube website.
The trend for tombstoning - jumping off cliffs, piers, harbour walls or other high points into water - has claimed a number of lives around the UK.
Anyone caught jumping into the river will be issued with a £50 fine.