How Do I Get The Water Stains Out Of My Emu Boots?

My emu’s now have these white water stains right at the toe, from wearing them in the rain. (My emu boots are chocolate brown, just in case that matters.) Does anyone know how i can get the stains out?
-(Emu boots, are just like uggs, only a tiny bit different, and no there not made out of emu’s.)