La Seine is the prizewinning ‘lyrical’ essay that re-established Joris Ivens on the Western scene […] and consolidated his Paris foothold. Its development and production were a triumph of networking within a conducive time and place. Since 1938, Ivens had nurtured his friendship with the influential Parisian communist film critic and historian, Georges Sadoul […]. Sadoul was behind the basic idea for La Seine, inspired by captions he had written for Parisian photos by Henri Cartier-Bresson and not surprisingly by Ivens’s own work on rivers in Das Lied der Ströme (Song of the Rivers, 1954) itself. Ivens requested the chance to develop the stalled treatment, and the two of them fleshed it out in long walks on the riverbank where they discovered they were both observing the same aspects of urban life along the famous river. […]
The resonances of the emergent hybrid ‘lyricism’ Ivens would effect in La Seine had much broader implications than his own individual personal aesthetic and career trajectory. It tapped a Zeitgeist, and the name of Ivens’s old acquaintance Vertov must now be brought back on this account to flesh out this claim. […]
It is not far-fetched, then, to concur with Sadoul about La Seine as an homage to Dziga Vertov’s ‘life-caught-unawares’ aesthetic, a revival of the kino-eye sensibility and exploration of the cinéma vérité doctrine. Ivens’s tactic of spontaneously, directly, and materially observing public social and economic life, and his film’s non-interactive close following of the everyday as it unfolded on the banks of the Parisian river, were a clear ricochet of the Vertov revival.[…]
Like the river itself, the finished La Seine is fluid, inexorable, majestic, vibrant with underwater eddies and kinetic tension. […] Speaking purely cinematically, the documentary offers a rich visual canvas of Paris social life, all from the point of view of the river’s paved banks, from its many bridges and, most importantly, from the water’s surface.

Thomas Waugh, The Conscience of Cinema. The Work of Joris Ivens 1912-1989, Amsterdam University Press-EYE Filmmuseum, Amsterdam 2016