The American Red Cross is urging people to donate blood after the national blood supply dropped nearly 25% in June.

The shortage comes as hospitals enter the summer trauma season, when emergency rooms often see more patients with serious injuries caused by traffic crashes, outdoor recreation, workplace accidents and other seasonal emergencies.

The Red Cross says blood distributions to hospitals are currently running nearly 3,500 units higher per week than expected. At the same time, donations have declined because of summer travel, temporary illnesses and the seasonal loss of school blood drives.

Trauma patients are among the largest users of donated blood. According to the Red Cross, a single crash victim can require as many as 100 units.

Blood is also needed for patients undergoing cancer treatment, people with sickle cell disease and mothers experiencing childbirth complications.

The Red Cross says securing appointments throughout July will be important to maintaining supplies of every blood type. Anyone who donates between July 13 and July 31 will receive a Fandango movie ticket.