Plastic fishing gear largely contributes to plastic pollution in our oceans. Biodegradable materials have been promoted as alternatives without consideration of their full impacts on the marine environment. In our 'blue' paper, we debunk the myths surrounding the biodegradability of plastics under marine conditions and highlight their potential negative effects on marine life and human activities. We call for a comprehensive international framework to address the full lifecycle of plastics in marine ecosystems, including those labelled as biodegradable.