The US blood supply is at a 15-year low, said the American Red Cross.
The organization said that it was 50,000 units short of its basic needs in June and will likely face another shortage in July.
According to NBC News, the reason for the sharp decline in donations is extreme weather and summer holidays for those in school.
The organization said that tornadoes in the Midwest have meant a dramatic rise in need, while waning student donations - 20 percent of the total - have been declining.
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The severe storms have also cancelled dozens of blood drives, which added to the shortage, said USA Today.
Another reason may be that an unusually hot summer has kept people indoors.
"We just aren't seeing the donors coming through the door right now," said Karen Stecher, a spokesperson for the Red Cross, according to USA Today.
The Red Cross reached a crisis level on June 25 this year.
"A lot of people are on vacations and people are taking a lot of time off, but patients never get a vacation from needing blood," said Ellen Russell, director of Red Cross blood services in Maine, reported NBC.