This week Matt Baker and Ellie Harrison are in the Lee Valley, the green lung of London. It has provided fun and fresh air for city dwellers for more than four decades but, as Ellie discovers, there is an incredible array of wildlife here too. She takes to the water to see what is being done to clean up its chalk streams and she discovers why common terns are making the Lee Valley home. As well as being its lungs, it is London's larder too, as Matt finds out when he meets the Sicilian siblings who have turned salad growing into a thriving family business. The Lee Valley is also home to the Olympic Water Park, where volunteers from the RNLI are busy carrying out an essential flood training exercise. Ellie finds out first-hand how important these mock drills are in saving people's lives. Down on the farm, Adam goes in search of a new Gloucester bull that will help improve his herd. There's little doubt that climate change is going to affect our future, but what about the present? Tom Heap looks for proof that it is already having a significant impact on the British countryside.