Bleach won't fix a smelly cooler.

Use a paste of baking soda and water, scrub the inside, let it sit for an hour, then rinse with white vinegar. That’s it.

Bleach kills bacteria but doesn’t neutralize the odor compounds—it just masks them. Vinegar and baking soda actually react with the smelly stuff (amines from fish, mostly) and turn them into something odorless. Works on plastic coolers, soft coolers, even Yetis.

For stubborn smells, leave the baking soda paste on overnight. Rinse well with water after the vinegar step. No soap needed—soap leaves residue that can trap smells later.

This is not where you need fancy marine-grade cleaners.