Almost all water around the Keys out past 3 nm is inside the Florida Keys National Marine Sanctuary. The sanctuary bans dumping 'any material' from inside its boundary, and ash scattering is not one of the exceptions, so you need a free-to-apply NOAA sanctuary cremation permit (online form at floridakeys.noaa.gov/permits/special-use.html). NOAA only permits ceremonies at least 3 nm from shore, in federal sanctuary waters; only ashes and flowers - no urns, boxes or plaques. Stay out of Sanctuary Preservation Areas and Ecological Reserves, where only engine cooling water and exhaust may be discharged. Atlantic side 3 nm off Key West is near the reef line (estimate); avoid Sand Key, Rock Key, Eastern Dry Rocks preservation areas and the Western Sambo Ecological Reserve. Key West Harbor has Navy (NAS Key West) and cruise-ship security zones. Gulf-side state waters extend 9 nm, so NOAA's 'federal waters only' wording may mean much farther out on the Gulf side - use the Atlantic side.