A running club sparked a security alert which resulted in part of a town centre being sealed off after it used flour to mark a route.
Hazardous material experts were deployed after the "substance" was spotted in King's Lynn, Norfolk.
Police said the running club had been given "words of advice", while event organisers apologised for the alarm.
The flour was found in Tuesday Market Place on Saturday, the Eastern Daily Press reported.
Part of the square was sealed off.
Police had previously appealed for help in identifying a man and a woman seen distributing a "substance from a carrier bag".
The flour trail had been sprinkled around the town by the Norfolk Hash House Harriers.
Its 20 members were joined by 40 runners from Oxfordshire's Bicester H3 branch.
After the security scare, event organiser Bob Green, of Kidlington, Oxford, said: "It was a bit of a surprise.
"It's good, harmless fun out in the fresh air, but in the summer we run in the countryside, so it's less of an issue. The trails are marked with sawdust.
"We have started to be more security conscious in informing neighbourhoods, but we apologise that on this occasion we didn't inform the police or council."
A blob of flour every 50m was spread around the town to mark out the route.
Hash House clubs, which describe themselves as "drinking clubs with a running problem", are popular with thousands of runners across the world. The athletes usually meet up in pubs after races.
A group of expats started the first club in Malaysia in 1938.
David Armes, 60, landlord of King's Lynn's Stuart House Hotel, has been a Hash House Harrier since 1983.
"People must have a good sense of humour and this has caused quite a laugh," said Mr Armes, who set up the trail.
"Sadly, the world is not the sort of place it was in the 1930s.
"It's a bit of a shame that a central police control room didn't know these runs happen every week."