The new seven-part series, the follow-up to 2001’s ‘Blue Planet’, uses new technology to get closer to the underwater action than ever before.
The series has been four years in the making and involved 125 expeditions in 39 countries.
But Sir David has revealed that filming some scenes was a “tragic sight”, in a day and age when the oceans have never been so under threat.
He says the most upsetting scenes are the evidence of bleaching of coral reefs.
The 91-year-old broadcaster also speaks of his frustration that more isn’t being done to deal with the eight million tonnes of plastic being dumped into the sea each year.
Last month, the BBC offered a first, breathtaking look at ‘Blue Planet II’.
Sir David narrates the five-minute film, which is made even more spine-tingling by the soundtrack, which comes courtesy of Hans Zimmer and Radiohead.
‘Blue Planet II’ begins on 29 October at 8pm on BBC 1