Eifion and his dog Sboncyn want to catch a delicious fish for their dinner. But, no matter how hard they try, all they manage to catch is other people's rubbish! Heading home with empty tummies, they meet some new friends who teach them about the problem of pollution in the ocean, and what they can do to help.

Mae Eifion a'i gi, Sboncyn, eisiau dal pysgodyn blasus i'w fwyta i swper. Ond, dim ots pa mor galed maen nhw'n ymdrechu, yr unig beth maen nhw'n llwyddo i'w ddal ydy sbwriel pobl eraill! Wrth anelu am adre â'u boliau'n wag, maen nhw'n cyfarfod ffrindiau newydd sy'n eu haddysgu nhw am broblem llygredd y môr, a beth gallan nhw ei wneud i helpu.