Poppy Merrymoss is competing in the Lily Pad Lake swimming gala with her best friends Rose Seedpip and Ninad Cleardrop. But nasty Lady Nightshade is determined to ruin the event and fills the lake with a thick algae that covers the swimmers in slimy green gunk. And even worse, the thick algae has trapped a frog family beneath the slime!Can Poppy and her friends clean the lake in time to save the frogs - and the gala?