With each new day and each new wave that rolls in, there is more rubbish in the sea. Sperm whale Lota wonders where all the rubbish is coming from. Lota and the crab Malacu decide to find out what's going on in the sea. Their investigations lead them first to a tourist boat and finally to the harbour, where they discover that plastic is dominating people's entire lives. The sea dwellers decide to launch an ‘Operation Clean Sea’ and collect the plastic waste. They get help from Sumi, the boat captain's daughter. But although they manage to clean the sea together, the operation does not solve the rubbish problem, as the land is now buried under rubbish from the sea.
Sumi begins to realise that there is only one solution...