The American Red Cross has issued an emergency appeal for blood donations.
The organization said it has less than a day's supply of type O blood, which has forced it to limit distributions to hospitals.
That could mean some patients may have to wait for surgeries or other treatments.
Type O positive blood is the blood type that about 85% of the U.S. population can be given in an emergency. About 15% of people can be given type O negative blood in an emergency.
Sydney Henry is with the Michigan region of the American Red Cross. She said the blood supply is often lower in the summer months, due to people traveling or being out of school, but this is worse. Henry said blood donations dropped 25% in June, and haven't recovered to normal levels since then.
"We believe that some of the things that have contributed to that, are things like extreme heat, and the recent air quality issues, particularly in Michigan," she said.
The widespread cyclosporidia outbreaks, which have sickened thousands of people, could also be a factor in the decline in donations.
