Residents of four Casco Bay Islands were without running water early Thursday because of a water main break between Great Diamond and Little Diamond islands.

Portland Water District customers on Peaks, Cushing’s, Great Diamond and Little Diamond islands experienced low water pressure starting around 4:30 a.m., said Michelle Clements, spokeswoman for the Portland Water District. Water pressure was back to normal by 8:30 a.m. because crews were able to isolate the break and use a second water main to supply water to the island.

Clements said it is fortunate that the break is in an area where the 8-inch water main crosses a sandbar. Crews fixed the water main at low tide and service to the islands had been restored as of 7 p.m., Clements said.

The water issue was brought to the attention of city officials early Thursday when a firefighter stationed on the island was unable to flush a toilet and soon realized the problem was more widespread, city spokeswoman Jessica Grondin said.