In Under Thin Ice, two divers, Jill Heinerth and Mario Cyr, tell us about their risky expedition to the Canadian Arctic. They had first intended to document arctic ecosystems and marine wildlife, but were faced with an unexpected reality. The Arctic is warming very fast and the animals are not where they used to be. Through their testimonies, Jill and Mario explain what causes the accelerated melting of the ice and creates climate change. They also discuss the impact of these phenomena on arctic wildlife and consequences for the whole planet. The first part of the film takes place in Lancaster Sound, 700 kilometers north of the Arctic Circle. The sea ice is already covered with water and threatens to break at any moment. But thanks to their Inuit guides, Jill and Mario brave the elements and manage to film belugas, narwhals and algae underwater. The second part brings them further south to Naujaat Bay. It takes days before they find walruses, when usually there should have been hundreds. But bears are everywhere and seem hungry. This does not stop Jill and Mario from filming the animals.