Let's start with the badly translated title. Where's the mermaid? There isn't one. The title character is a rusalka, not a mermaid in any western understanding of the word. Rusalki are the damned souls of girls who commited suicide by drowning, typically because they were pregnant out of wedlock and abandoned or rejected by the father. Such a girl becomes a rotting half-fish, half-woman, hideous in appearance, inhabiting ponds and rivers (not the ocean), who tries to lure young men to their death. They can shape-shift to appear beautiful or take the form of a living person. They are vengeful, evil, capable of sorcery, and dangerous. Don't think Ariel in a clamshell bra. Think carp zombies.
There. Does that help?
Marina is engaged to Roma, a competitive swimmer. Roma and his sister Olga lost their mother at an early age, supposedly to drowning. But as you see in the opening scene, she was actually killed by a rusalka at their lakeside dacha (summer house). The widowed father, who has had at best a distant relationship with his children ever since, unexpectedly gifts the dacha to Roma and Marina as a wedding gift, telling them to sell it and take the money. Instead, Marina wants to fix it up and keep it. But the rusalka has not gone away, and now casts her eye on Roma...
Visually, "The Rusalka: Lake of the Dead" (to give it its proper translation) excels. It is rich in old-fashioned atmosphere: mist on the lake, moon through clouds, candlelight in the old banya (wooden sauna), a lush Russian forest.
Contrary to what some reviewers found, the storyline is perfectly coherent. There are a handful of cultural references that Russians will understand but are not explained for the benefit of westerners (such as a shout-out to Karamzin's "Poor Liza").
But these do not pose a problem as long as you understand that a rusalka is not a mermaid.
