The Boundary Waters Canoe Area Wilderness will close on Tuesday as wildfires burn amid an active heat wave in northern Minnesota. Visitors with overnight paddle, overnight motor and overnight hiking permits who were intending to enter the forest between Monday and Friday will have their reservations canceled. Day use motor reservations with entry dates of Tuesday through Friday were also canceled. Full refunds have already been processed, forest service officials said. The closure impacts all entry points to the BWCAW. The announcement comes two days after the U.S. Forest Service closed 225,000 acres of the region. Crews are going campsite to campsite in canoes to ensure that visitors are evacuating, according to Deputy Forest Supervisor Drew Stroberg. He anticipates that it will take a week for them to sweep every campsite. According to the U.S. Forest Service, a series of lightning strikes on Tuesday lit 21 fires, and over the course of the last few days, the size of the wildfires have grown due to high temperatures and strong winds. Two of the fires could cross into Canada, and officials said they're keeping an eye on one across the border that could move into the U.S. The Thumb Fire has already consumed 5,000 acres, and forest service officials believe that it will burn in some capacity until snow falls in the autumn. Officials said that while they intend to keep the Boundary Waters shutdown "as short as possible," they anticipate that some areas of the forest will stay closed for the remainder of the season. The Minnesota Pollution Control Agency also issued an air quality alert for Two Harbors, Hibbing, Ely and Tribal Nation of Grand Portage that takes effect at 7 a.m. Tuesday and runs until 11 a.m. Thursday.