Bleach is your friend.

Bleach. Soap and water won’t cut it. Fish oils and proteins bond to plastic, and only bleach breaks them down.

Fill the cooler with a gallon of water plus about a quarter cup of bleach. Let it sit for an hour (or overnight if it’s really bad). Rinse thoroughly. Let it dry in the sun with the lid open. Sunlight kills the remaining odors and bacteria.

The real secret: always dry it completely before storing. Moisture breeds the smell faster than any fish ever could. Cracking the lid open for a day after cleaning prevents that trapped-rotten air.

Future You will thank Past You. Nobody wants to open a cooler and smell last week’s catch.