By the Bluest of Seas (Russian: У самого синего моря, romanized: U samogo sinego morya) is a 1936 Soviet romantic comedy film by Russian director Boris Barnet. It is his second sound feature. Starring Yelena Kuzmina, Nikolai Kryuchkov, and Lev Sverdlin, the story centers on a love triangle between two castaways and a woman from a collective farm on a Soviet Azerbaijani island in the Caspian Sea.

Modern critical reviews have hailed By the Bluest of Seas as a little-known classic of Soviet cinema. Although some critics have noted that the story and characters are thinly written, high praise has been directed toward Barnet's direction and cinematography, his innovative use of sound, and the film's footage of the Caspian Sea. Some have perceived pro-communist propaganda within the film. However, many consider the film to be less politically overt than was common in Soviet cinema of the time. This, along with the film's divergence from the era's defining style of Socialist realism, has led many to view the film as unique. It has been reported that Barnet found himself in trouble with Joseph Stalin for these reasons.

The film has long been elusive to Western audiences. It was never released on any home media format, until 2012, at which point it was made available by the Russian publisher Ruscico and the UK publisher Mr. Bongo Films.