Police have criticised plans for 3,000 people to float on inflatables down the River Tyne while drinking beer.
The event, publicised on Facebook as the River Tyne Booze Cruise, is planned for July 1 starting in Newburn, Newcastle, and ending three-and-a-half hours later on the Quayside.
Organisers insisted the idea was not a hoax and said it was based on a Finnish event.
They posted a video of scores of young Scandinavians drinking beer in inflatables while floating serenely down a tree-lined stream.
The Facebook post, shared almost 10,000 times, includes the message: "1 rule: Stay in your craft at all times to eliminate accidents.
"Armbands / life jackets highly recommended"
Northumbria Police said they were concerned about safety and will speak to the organisers.
A force spokesman said: "The River Tyne is not a countryside stream.
"The current is strong, there is a lot of debris and a number of vessels use the waterway every single day.
"A rubber dinghy is not an appropriate vessel to be used on this river and if people were to fall overboard then they could find themselves in real danger.
"If those involved are then consuming a significant amount of alcohol then that causes further concerns that could lead to a significant incident.
"We understand people want to enjoy the summer and have fun but we have a duty to ensure the safety of the public and put appropriate measures in place."