Critics’ choice

Blue Planet II (BBC1, 8pm-9pm)

Film crews have spent four years scouring the seas, mounting 125 expeditions and visiting 39 countries to find a fresh cast of aquatic animals that will blow our minds once again. Tonight’s first episode takes us on a journey from the intense heat of the tropics to our planet’s frozen poles. In the tropics, dolphins surf for what looks like sheer pleasure, while in temperate seas, mobula rays create an enchanting display at night. Meanwhile, off New Zealand, two separate species – false killer whales and bottlenose dolphins – gather together to make a formidable army and take advantage of a glut of fish.

Great Canal Journeys (Channel 4, 8pm-9pm)

Timothy West and Prunella Scales return to their canal boat for another series of journeys, beginning in the Norfolk Broads. This is the first time the couple have visited the area, and they learn about the unique way of life that has developed over the centuries in this network of slow-moving rivers, fens and marshes.

Louis Theroux: Talking to Anorexia

(BBC2, 9pm-10pm)

It affects one in every 250 women, and now anorexia, the pathological fear of eating and gaining weight, is the most deadly mental illness in the UK. For his latest investigative documentary, Theroux heads to two of London’s biggest adult eating-disorder treatment facilities.