Fat Bear Week is back.

The National Parks Service is asking voters to weigh in on who is the biggest bear in Katmai National Park and Preserve.

Photos from National Park Service via Facebook (R.Jenson/J.Cuomo)

Now in its fifth year, the contest features the bears made famous by the Katmai webcams at Brooks Falls. The NPS says millions of viewers from around the world watch the bears fish for salmon.

Starting Wednesday, viewers can vote their favorite bears on the Katmai Park's Facebook page.

Each day, two bears will be posted on the page, and viewers vote on who is the fattest. The winning bruins move on to the next round, and the 2019 final winner will be announced on Fat Bear Tuesday — Oct. 8.

Photo from National Park Service via Facebook (N.Boak/L.Carter)

The park service says around this time of year brown bears at Brooks Falls eat constantly, building up stores of body fat that will help them survive winter hibernation, which can last half the year.

During hibernation, a bear can lose up to a third of its body mass, according to NPS.

Katmai has one of the world's largest concentration of brown bears. 

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