Christopher Mouse and the submarine

Christopher the mouse's biggest dream is to see what lies beneath the surface of the river. One day, he discovers a small submarine on the bank. A child's toy, just the right size for a mouse. All he needs to do is fix it, restock the supplies, and he can embark on a daring aquatic adventure.
But what's this? Excitement turns to horror. The great mouse adventure turns into a rescue mission. An eel is tangled in old netting, little fish are trapped under a pile of junk… The river has become one giant rubbish dump!
Will Christopher manage to save his new friends in trouble and clean up their beloved river with them?