"With current technology, no part of the ocean remains too deep, too remote, too difficult to fish. As a result, the greatest threat to our oceans is overfishing," Roger Rufe, president of the Ocean Conservancy, said.

"As certain species of fish disappear ocean ecosystems decline and this effect can have repercussions on all Americans as far-reaching as pollution or global warming," he added.

Of the U.S. fish stocks that have been assessed, nearly half are depleted or overfished, including Pacific salmon, Gulf of Mexico red snapper, Gulf of Maine cod and swordfish, according to the report.

Other marine life is also in danger, the group said.

Only an estimated 300 North Atlantic right whales still exist, and all six species of sea turtles found in U.S. waters are threatened or endangered, it said.

Pollution has left 44 percent of tested U.S. estuaries unfit for swimming or fishing, according to the report.

The Ocean Conservancy also called for stricter enforcement of the Clean Water Act to curb polluted runoff into oceans and to overhaul the nation's fishery management system.