Perhaps the best description of this kind of summer scene comes from the book Edo meisho zue (Illustrated guide to famous sites of Edo, 1829-1836):

The 'cooling' season at this location begins on the twenty-eighth of the Fifth Month and concludes on the twenty-eighth of the Eighth Month. The area is always lively, but it is at its height during the summer months. The shore is crowded with misemono attractions; their advertizing banners flap and flutter in the breeze. Lofty mansions and tall towers frame the river along both banks; benches of the tea pavilions line the water. Lantern lights sparkle charmingly, reflected in the stream. Cabin boats and open boats crowd the current; moored together, they conceal for a moment the entire flow, and it is no different from dry land. Music of strings, songs, drums, and flutes echoes noisily in the ear--truly, Great Edo at its most glorious!
(Source: Andrew Markus, "The Carnival of Edo: Misemono Spectacles from Contemporary Accounts," Harverd Journal of Asiatic Studies 45 (1985):509)

Join the moshing on the bridge by clicking on it.