Untreated sewage, garbage, fertilizers, pesticides, industrial chemicals (ect.) most of the pollutants on land eventually make their way into the ocean, either deliberately dumped there or entering from water run-off and the atmosphere. Not surprisingly, this pollution is harming the entire marine food chain - all the way up to humans.
how it is being resolved? Humans are beginning to see the shortsightedness of the "dumping" philosophy. Many national laws as well as international protocols now forbid dumping of harmful materials into the ocean, although enforcement can often be spotty. Marine sanctuaries are being created to maintain pristine ocean ecosystems. And isolated efforts to restore estuaries and bays have brought some success.