The annual grassroots event Kaljakellunta invites people to float leisurely down a river and enjoy beer. Eastern Uusimaa police estimate that about 600 people participated in the 2019 event, a significant decrease from previous years when more than 2,000 revellers were estimated to have joined in.
Officials say that chilly temperatures on 3 August likely discouraged many from partaking in the fun.
This year's procession departed from the Heureka science museum and followed the Kerava River. The float alternates every other year between two rivers in the cities of Helsinki and Vantaa.
Police say Saturday's float proceeded peacefully. Only one inebriated individual was taken into custody.
Every year since the event was founded in 1997, participants in the beer float have been upbraided by law enforcement officials, environmental groups and local residents for leaving their rubbish on the shores. Cans, bottles, abandoned plastic boats and inner tubes, and other trash cause damage to the waterways' natural environment.
Organisers arranged a clean-up effort on the day after the event for the first time in 2017.