New hat, got wet, smells TERRIBLE?

I bought my finance new hat from lids. It's a zephyr fitted hat- ND if it matters... He wore it once! It got damp from the rain and smells so horrid that we can not even keep it in the room! It smells like a combo of rotten fish and feces! He didn't sweat in it and he showered before he wore it! I plan on taking it back but just in case they don't replace it, I need to know how to remove the smell. Obviously getting it wet will make it worse- that's what started the smell in the first place. Has anyone else had this problem? It's 97% Acrylic and 5% spandex. Made in Bangladesh.