Thanks to the NSSF – National Shooting Sports Foundation I share a  link they provided:

http://www3.nssf.org/share/pdf/SAAMI-Ammunition_Exposed_to_Water.pdf

An Excerpt from the PDF above.

“Regarding ammunition that has been submerged in water for any period of time, there are too many variables that would need to be considered such as the cartridge type (e.g., rimfire, shotshell, centerfire rifle, centerfire handgun); depth of the water; length of time the cartridges were submerged; are the primers on the cartridges sealed providing some degree of water resistance? what contaminates may have been in the water that might affect the powder charge or priming compound? and many others. ”

In short, the Sporting Arms and Manufacturing Institute, Inc. does not recommend use of ammo submerged in flooded areas and to dispose of it by contacting your local law enforcement office.