DULUTH, Minn. — An increase in bear activity has caused officials to close part of a national park in northwestern Wisconsin for up to two weeks.

Sand Island, one of the Apostle Islands, was closed to overnight camping on Monday because of bears entering campsites on the hunt for human food. Park employees thought a temporary halt on camping would reduce food and bear activity.

But some daytime visitors who left food packed in a cooler in their beached boat Wednesday — which is an appropriate thing to do — discovered a bear repeatedly entering the boat when they left it, said Apostle Islands National Lakeshore Superintendent Bob Krumenaker.

"The bear is very assertive; it's not afraid of going where people are," he said. "He does run away when people make noise or try to scare him, but that doesn't last very long."

Krumenaker said Friday it could be a week or two before the island reopens. He said they've reopened other islands with similar situations too early and the bears returned and they had to close again.

"We first have to remove people and food and give the bear time to start remembering food is natural in the environment, he said.

The increased bear activity is likely due to the prolonged cool weather and lack of ripe berries, he said.

It's not known whether it's the same bear or multiple bears, Krumenaker said.

Federal budget cuts could prolong the closure because they have fewer people to educate campers on the correct way to store food when there are bears nearby, he said.

Some of the behavior that prompted the nighttime closure included a bear breaking into a tent for food and a bear poking his head inside the door of a tent with people inside.

"He's not done anything aggressive towards people and we want to keep it that way," Krumenaker said.

Cameras have been installed to help determine the number of bears on Sand Island.

They also are working to "give the bear a hard time," he said. That means making noise and throwing non-harmful things at the bear to make it think people are not who it wants to be around, Krumenaker said.

It's important that visitors to the other islands be careful about making sure food isn't left unattended, Krumenaker said.