Marine Pollution (MARPOL) 73/78 is an International Convention for the Prevention of Pollution from Ships, the 73 and 78 stands for the year of 1973 and 1978.

objectives: Pollution shall be avoided to preserve the human environment in general and the marine environment in particular

Goals: Complete elimination of pollution and minimization of accidental discharge

MARPOL 73/78 has 6 annex, those are:

Annex I, Prevention of Pollution by Oil

Annex II, Regulation for the control of Pollution by Noxious Liquid Substance

Annex III, Regulation for the control of Pollution by Harmfull Substance Carried by Sea in Package Form

Annex IV, Regulation for the control of Pollution by Sewage from Ship

Annex V, Regulation for the control of Pollution by Garbage from Ship

Annex VI, Regulation for the control of Pollution by Air Pollution from Ship

It is then clear stated that every water at sea level pollution is dominated by Sea discharge. Here are some reference about MARPOL, we can use well:

(http://www.imo.org/About/Conventions/ListOfConventions/Pages/International-Convention-for-the-Prevention-of-Pollution-from-Ships-(MARPOL).aspx)