In anticipation of the Fukuoka Daiei Hawks winning the Pacific League pennant, the Fukuoka Prefectural Government on Friday increased the number of "Do not dive" warning signs along the city's Naka River.
Officials set up more signs along a bridge over the river in the city's Nakasu district, which is Kyushu's largest night spot.
Some 900 fans dove into the Naka River when the Hawks won the league pennant in 1990 and 2000, with some suffering injuries, according to local police.
The prefectural government had set up one warning sign on the bridge. Officials added four more Friday.
The government has also checked the depth of water in the area, acknowledging that fans will probably dive regardless of the presence of warning signs.
The prefecture's move apparently reflects concerns over a Hanshin Tigers fan's fatal plunge into the Dotonbori River in Osaka on Wednesday night.
While celebrating the Tigers' first Central League pennant in 18 years, 24-year-old Masaya Shitababa was either pushed or dove into the river and later found dead.
Police are investigating the case as a possible assault resulting in death following witness reports that a man was seen pushing Shitababa from the bridge.
Some 5,300 people jumped into the river Monday night, when the Tigers won the pennant, Osaka police said.