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9 deer in a sacred sanctuary in Japan have been found dead with plastic in their stomachs

(CNN) Nine deer in Nara, Japan, have been found dead with plastic bags in their stomachs, according to the group that monitors the welfare of the deer.

Over the past five months, nine of the 14 deer that died in the famous park were found to have plastic bags filling their stomachs. In March, the group posted a picture of more than 7 lbs of plastic bags that were found inside one dead deer's stomach.

Yoshitaka Ashimura, secretary general of the Nara Deer Preservation Foundation, confirmed that three of the deaths were directly related to digestive issues from eating the plastic.

More than 1,000 of the sacred Sika deer roam around in Nara Park and are classified as a national treasure in Japan. The park is also home to multiple temples and shrines. Tourists are advised to only feed the deer rice crackers, which are known as Shika-senbai.

How to (safely) enjoy Japan's famed deer park

The group alerted tourists not to throw away plastic bags in the park because the deer can smell the food left in them and will eat them. Ashimura said there are also signs around the park in multiple languages saying to not throw away plastic bags, but they have not been successful in preventing the practice.

In response to the alarming number of deaths, the Nara Deer Preservation Foundation launched a cleaning campaign on Wednesday, the first in eight years. More than 100 volunteers pitched in and rounded up over 116 pounds of trash, 70 pounds of which was plastic.

"The amount of plastic garbage we collected was over our expectation," Ashimura said, "We are concerned that a mere clean up won't solve the issue. It's important that the visitors won't throw them away to begin with to protect deer."