The Making of <i>Blue Planet II</i>’s Incredible Deep Ocean Episode

There are lakes at the bottom of the ocean. These are places where the water contains far more salt than usual, making it extremely dense. It sinks, pools, and refuses to mix with the surrounding seawater, creating perception-defying lakes that, despite being hundreds of meters deep, have their own surfaces and shorelines. One such lake features in “The Deep”—the second episode of Blue Planet II, which aired Saturday on BBC America and other networks. Illuminated by submersible headlights, and accompanied by choral music, cutthroat eels wriggle from the “shores” of the lake and dive into its midst for reasons unknown. Some are so overwhelmed by the salt that they go into shock, their sinuous bodies twisting into convulsing knots.

Two weeks ago, I described as the “.” I stand by that, and I’m also crowning “The Deep” as the greatest of the series’ seven episodes. It follows in the tradition of the original from 2001, which also voyaged into the abyss for its second episode. The result was