Kate Humble presents a celebration of the UK's surprising and beautiful marine life and takes an in-depth look at the issues affecting our coastal waters. From Cornwall to Scotland she reveals breathtaking marine animals - dolphins, otters, and colourful fish that look almost tropical. Kate gets wet, too, when she swims with Britain's biggest fish - the huge but gentle basking shark. We find out what we can all do to help conserve and enjoy this wildlife - how simple changes in our appetite for fish and chips could literally save the UK's fishing industry. And good news, too - there's a new Marine Bill that could be the most significant turning point for our UK sea life ever.