The American Red Cross has declared a national emergency as blood supplies run low.

The disaster relief nonprofit is urgently asking for help after blood donations fell to a four-year summer low. It is specifically seeking type O donors, as their blood is the most widely compatible.

This is only the second time in the American Red Cross’ 85-year history of collecting blood that it has declared a national blood supply crisis. The first was in January 2022.

Thousands of people are already donating blood, but the American Red Cross said it can’t keep up with hospital demand during what it called the “summer trauma season” in a Monday news release.

“Extreme heat, poor air quality and widespread foodborne illnesses are contributing to lower donor turnout this summer, further straining the nation’s blood supply,” the release read.

Temperatures have regularly topped 100 degrees in the Northeast this summer, and the region has also seen smoke from recent Canadian wildfires, keeping people indoors.

The country is also dealing with a cyclosporiasis outbreak this summer, in which an explosive diarrhea-inducing parasite has infected thousands and hospitalized hundreds of people.

While all eligible donors are urged to give blood, the American Red Cross emphasized that those with type O blood are the most needed.

The American Red Cross, the country’s largest single blood provider, now has less than a one-day national supply of type O positive blood. This has caused the nonprofit to begin limiting distributions of type O blood to hospitals.

About 60 percent of the blood that the American Red Cross supplies to hospitals is type O blood. Type O positive, which is the most commonly transfused blood type, can be given to roughly 80 percent of patients, and type O negative can be given to virtually anyone.

“Following our first-ever national blood crisis in 2022, we put additional safeguards in place to help prevent a crisis like that from happening again. But this summer, blood donations simply are not keeping pace with hospital demand, and inventories — especially type O blood — remain under significant strain,” Chris Hrouda, president of Red Cross Biomedical Services, said in a statement.

“Every donation has the potential to help save lives, and we urgently need everyone who is eligible to make an appointment to give blood as soon as possible.”

Just three more donors at each blood drive this summer can end the national blood supply crisis, the nonprofit said.

Beyond relying on donors’ goodwill, the American Red Cross is offering gifts to boost the blood supply.

Anyone who donates blood by Friday will receive a free Fandango movie ticket for up to $15. Those who donate in August will get a $20 Amazon gift card.

Those who wish to donate blood can make an appointment using the Blood Donor App, visiting RedCrossBlood.org or calling 1-800-RED CROSS (1-800-733-2767).