Bristol Bay, Alaska

A stream flowing toward Bristol Bay, Alaska in 2003.

This week, President Obama permanently banned oil and gas development in Alaska's Bristol Bay, one of the most productive fishing grounds in the country. The protected region supplies more than 40 percent of the seafood caught in the United States, and the rich waters support millions of seabirds and 25 species of marine mammals, including beluga whales, gray whales, and Pacific walrus, according to the Pew Charitable Trusts.

Bristol Bay off-limits to oil drilling

Pacific Walrus at Cape Peirce at Bristol Bay on Alaska's southwest coast. Federal wildlife biologists have erected a 250-foot-long fence to stop Cape Peirce walruses from accidentally plunging off cliffs to their death on an Alaska beach.

Pacific walrus are frequent visitors to the beaches in Bristol Bay.

Bristol Bay off-limits to oil drilling

Jason Kolhase on the Juneau, Alaska registered fishing vessel Icy Bay takes tension off the corkline so crewman Chris Miller, right, can remove a sockeye salmon from their net in the Egegik district of the Bristol Bay sockeye salmon fishery, July 15, 2009.

In 2009 the sockeye harvest run was over 50 million, a number that came faster and earlier than fishermen and biologists expected.

Bristol Bay off-limits to oil drilling

Sockeye salmon are seen in Bristol Bay, Alaska, in an undated handout picture provided by the Environmental Protection Agency (EPA).

Large-scale mining in the Bristol Bay watershed poses serious risks to salmon and native cultures in this pristine corner of southwest Alaska, the U.S. Environmental Protection Agency said in a report released in January 2014.

Bristol Bay off-limits to oil drilling

Fishing skiffs line the shore in New Stuyahok, Alaska.

Bristol Bay off-limits to oil drilling

Sockeye salmon are seen in Bristol Bay.

The largest wild sockeye run in the world funnels into Bristol Bay, according to the Pew Charitable Trusts.

Bristol Bay off-limits to oil drilling

Fish hang on a rack as they are dried in Koliganek, Alaska.

Bristol Bay off-limits to oil drilling

The Upper Tularik Floodplain in the Bristol Bay watershed.