Last week, the U.S. Environmental Protection Agency unveiled a long-awaited plan to clean up the Portland Harbor—and was met with disgust from environmental watchdogs.

It might seem strange that environmentalists would be unhappy about finally getting a federal plan to clean up one of the most polluted places in Portland—the Superfund site on the riverbed of the Willamette.

To understand why, look no further than the fish living in the harbor: carp, smallmouth bass, bullhead and crappie. Those fish dine on invertebrates living in river sediment—dirt tainted with toxic chemicals, including arsenic, mercury, and even perchlorate, the main ingredient in rocket fuel.

A 2009 study found that, in many scenarios, people eating fish from the harbor face cancer risks as much as 100 times higher than the EPA's guidelines. The EPA suggests people eat no more than five Willamette River fish a year.

Cami Grandinetti, manager of the EPA's regional Superfund remedial cleanup program, says that by the time the proposed cleanup is completely finished—an estimated 30 years from now, in 2046—citizens should be able to eat 20 harbor fish per year without elevated cancer risk.

But environmentalists are angry because the EPA's plan—which would cost $750 million—would mean perpetual limits on fish consumption.

"They're trying to make the case, 'Oh, well, there's some contaminants upstream that mean that we can never lift the fish advisory,'" says Travis Williams, executive director of Willamette Riverkeeper. "They have very little data to show that. I mean, paltry amounts of data."

How many Portland Harbor fish you can safely eat each year by 2046: