Jet efflux
When working on an hotel barge in Burgundy with American guests ( bit of a change from flight testing at Dunsfold ) the canal ran right past the end of the runway for the Dijon Mirage 2000 base.
The b----ds took great delight in blowing everything not bolted to the deck straight over the side !
I enjoyed it & had my camera ready, but it got a mixed reception from the passengers - I had warned them...