The National Parks Board (NParks) said it has been working with Hash House Harriers to reduce the practice of marking out running routes, even before a group left flour at Woodleigh MRT Station on Tuesday and sparked a security scare.
Responding to queries from The Straits Times, Mr Wong Tuan Wah, group director of conservation at NParks, said: "NParks regularly meets Hash House Harriers to advise on the rules regarding 'hash' running in our managed areas."
Hares, or runners who set the trail, mark it out using flour, chalk or toilet paper so that the other runners can pick up the "clues" and follow the route.
One man was arrested and two others are assisting with police investigations after flour left at Woodleigh MRT Station led to the station being closed for more than three hours and police and Singapore Civil Defence force officers being deployed.
In a statement issued on Wednesday, the Seletar Hash House Harriers apologised to the public and the authorities for the alarm and inconvenience caused.
Mr Wong said that chalk and flour are prohibited in NParks-managed areas as these are more "difficult to clean up, might seep into and cause damage to the environment". If consumed, these substances might also have detrimental effects on wildlife, he added.
"Only toilet or tissue paper are allowed to be used as markings, and they must be cleaned up immediately after the event," he said. "If they are not cleaned up, enforcement action could be taken."