Two inches of rain fell across the Allegheny Reservoir watershed on Tuesday.
That put a lot of new water behind Kinzua Dam.
The reservoir level was up about two feet from Tuesday morning to Wednesday morning.
According to Doug Helman, U.S. Army Corps of Engineers Kinzua Dam resource manager, the surface area of the reservoir is more than 26,000 acres. But rain falling anywhere within the surrounding 2,180 square miles drains to the reservoir. There are about 640 acres in a square mile - so the watershed covers almost 1.4 million acres.
"We got about two inches of rain," Helman said. "The reservoir's coming up. We need to bring the level down so we have storage for the next rain event."
The water level had not fully recovered from the previous rain event, he said, adding, "We were still a little bit high. The lowest we got was right at 1,329 (feet)."
Corps of Engineers officials are releasing that water and warning people who use the river for recreation that flows will be higher.
"Significant increase in outflow from Kinzua Dam are planned for Aug. 13 and 14," according to a Wednesday press release. "This increased flow may cause substantial rises in river levels downstream from the dam. Boaters and anglers are advised to exercise caution during the next few days."
The published outflow Tuesday morning was 3,260 cubic feet per second and the pool level was 1,328.97 feet above sea level.
At 8 a.m. Wednesday, the numbers were up to 3,390 cfs and 1,330.54 feet.
According to the Kinzua Dam Facebook page, the outflow Wednesday was increased to 6,400 cfs at noon and to 8,050 cfs at 3 p.m.
"We're going to open to a little over 12,000 cfs tomorrow (Thursday)," Helman said. "Hopefully we'll bring it down in time for the next rain event. It takes three or four days."
The outflow will change conditions for fishermen and boaters.
"It's going to raise the water downstream," he said. "There's no impact on property."