is it against the law to throw ashes in the ocean
The United States is similar to many countries which permit the spreading of cremation ashes within their Exclusive Economic zone: when spreading ashes from a ship which is registered in a different country, the regulations and reporting procedures for the ship's flag state need to be complied with once the vessel is in international waters, that is, outside 12 nautical miles. Ships follow the London convention principles, as opposed to MARPOL regulations, as the ash is intentionally taken on board for discharge at sea, as opposed to ash generated on passage from the ship's incinerators. It should be further considered that on 1 January 2013, MARPOL Annex V came into force, which prevents discharge of a ship's incinerator ash.
Burial at sea