Water Worlds

S1, E5: From our Scottish lochs and golden reed beds to southern swamps and the ponds of our back gardens, Britain's "Water Worlds" are wild corners we rarely explore - but they are the most biodiverse places in Britain. The film opens with intimate views of a family of beavers in Devon. Hunted to extinction 500 years ago, these reintroduced rodents are returning to our waterways. We discover how these natural engineers alter their landscape not only to help themselves - but also to the benefit of other species. Ponds and lakes are the domain of our largest reptile, the grass snake. These two-metre predators are perfectly adapted to hunt in the shallows. On their menu are amphibians. We join a breeding frenzy of toads - but discover that their amorous intentions can have disastrous consequences. Water voles are also vulnerable to snakes. But they're more worried about each other... The Reed Warbler has gone to extraordinary lengths to avoid being eaten, building an intricate nest suspended in the reeds. But it's vulnerable to a more insidious killer - the cuckoo. We witness extraordinary scenes as a blind cuckoo chick ejects its adoptive siblings from the nest. Our wetlands are rich in insects and other creepy crawlies. We witness the magical moment a dragonfly emerges from its larva, and discover a rarely-seen mass roost in the Somerset Levels. Below the surface we find a Water Spider - as she undertakes the remarkable and time-consuming task of constructing her very own silk-lined SCUBA tank. October signals the arrival of millions of birds in our wetlands. In Pembrokeshire, huge flocks of starlings join the cattle for dinner, before they head off to the reed beds to sleep. But before they tuck in for the night they put on a breath-taking performance - not for show but to avoid the peregrine falcon lying in wait.