On March 18, 2012, Sunday, To mark the 700th anniversary of Asakusa Sanja Matsuri Festival in 2012, a boat procession was held on Sumida River on March 18, 2012 (浅草三社祭斎行700年祭 舟渡御). The last time they did this was in 1958. The three portable shrines were first carried from Asakusa Shrine to neighboring Sensoji temple on March 17 where it stayed overnight. On the 18th, they were carried outside and a procession around Asakusa was held in 1312. The procession included Asakusa geisha and White Heron Dancers. They reached the pier on Sumida River at 12:30 pm and boarded the boats. They cruised all the way to Ryogoku and back.
A large crowd turned out along the river to watch this unusual event. The Sanja Matsuri originated as a boat procession on the river since it celebrates the three people who found the Kannon statue in the river and started worshipping it in Asakusa.
More photos: https://photoguide.jp/pix/thumbnails.php?album=840