Friends in the Cambridge area, or with an interest in its history, may enjoy this short 1947 informational film, Draining the Fens, at the East Anglian Film Archive.
Now, I’ll grant you, that doesn’t sound like the most gripping movie title, but this one is only nine minutes long, and if you’ve ever driven across the East Anglian countryside pondering the networks of rivers and drainage dykes, this explains how they came to be, and what can happen when they go wrong.
(The audio is a bit dodgy at the start, but improves.)