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FAIRBANKS — A plan to raise the water level in one of the Interior’s largest lakes is working.

Harding Lake rose more than a foot this summer, thanks to heavy rain in July and early August and a man-made diversion project built more than a year ago to funnel more water into the lake from a nearby creek.

“I’m sure Mother Nature deserves more credit than we do,” said Jeff Durham, programs administrator for the Salcha-Delta Soil and Water Conservation Service.

Torrential rain in late July and early August pushed the Tanana River over its banks and caused extensive flooding in the Interior. The resulting runoff from that rain also produced a significant rise in 2,500-acre Harding Lake, a popular recreation and fishing lake about 45 miles south of Fairbanks.

Between May 15 and Aug. 19, the water level in Harding Lake rose about 17 inches, reported John Fox, a forest hydrologist in the Forest Sciences Department at the University of Alaska Fairbanks. Since then, it has dropped about 1.5 inches, he said.

The rise in water is obvious, Fox said.

“There’s water where there wasn’t water last year and the year before,” said Fox, who has been monitoring the lake level for several years to study evaporation rates.

During a particularly wet seven-day span from July 28 to Aug. 4, the lake rose 9 1/4 inches, Fox said. The stream flow in the creek at one point during that period was measured at 22 cubic feet per second compared to a normal flow of 2 to 4 cfs, according to hydrologist Jim Vohden with the Department of Natural Resources.

“It was pretty spectacular,” Fox said of the rapid rise.

Jeff Cook, with the Harding Lake Homeowners Association, said the increase in the water level is noticeable to residents who live along the edge of the lake.

“You can tell by looking at it, no question,” Cook said. “Before this summer, I’d go out to the end of my dock and I would be lucky to be below my knees. Now, it’s up to your chest. It made an incredible difference.”

Mike Doxey, who owns a cabin on the east edge of the shore, said water is covering a good chunk of shoreline behind his house that was dry this spring.

“I have 700-and-some feet of beach out there, and it brought it in about 200 to 250 feet,” Doxey said. “It’s back to where it was a couple years ago.”

The water level in Harding Lake had dropped 2 1/2 feet in recent years, erasing more than 200 acres of valuable northern pike spawning habitat and rendering the docks of some cabin owners along the lake shore as useless. The drop in water prompted a cooperative effort among state agencies and federal agencies and local residents to restore the water level to historic levels.

Using $400,000 in federal funding, a dam of sorts was built at a fork in Rogge Creek, a feeder creek about a mile and a half from the lake, to help steer more water into the lake. The diversion project was installed in the spring of 2007 and resulted in a rise of about 4 inches in the lake level prior to this summer’s deluge.

A total of 4.12 inches of rain fell in July — the fifth-wettest July on record — and another 2.66 inches of rain fell in the first two weeks of August. For the summer, 8.88 inches of rain fell at the Fairbanks International Airport, which is almost twice the normal amount and the sixth-greatest June through August rainfall total on record.

While there is no way to gauge how much the diversion project contributed to the meteoric rise, it undoubtedly helped, Durham said.

“It maximized the opportunity we had this summer,” he said.

Scientists don’t know how much water evaporates and how much seeps out of the lake, which is what Fox is trying to figure out. How quickly the lake rises depends on rainfall and snowfall, he said.

Experts originally speculated it would take up to 10 years to bring the lake back up to historic levels. While another summer as wet as this year’s isn’t likely next year, Durham said it may not take as long as originally thought.

“It gets us a lot closer to the target mark than we anticipated,” he said.

The fact that the diversion project withstood the torrential rain and ensuing flooding also gave those associated with the project reason to cheer. They worried the whole thing might wash away.

“There’s so much silt there that we were worried about erosion. ... We were very concerned about that,” Durham said. “We were quite pleased that it weathered all that flooding very well. This was a big test for us.”

Even though the lake rose a foot this summer, it will take considerably more water to restore the pike spawning habitat that was lost when the lake dropped, said Audra Brase, a Fairbanks-area sport fish biologist with the Department of Fish and Game.

“We’ll see what happens in the next couple years,” she said. “Pike don’t need a whole lot of water to spawn, just a couple inches over their backs.”

The state closed the lake to all pike fishing in 2000 when the population plummeted as a result of overfishing and lack of production because of a loss of spawning habitat. It will take several years for the pike population to replenish to the point where the state can reopen the lake to pike fishing, Brase said. A management plan dictates when the department can loosen restrictions on pike fishing in the lake and any changes must be approved by the state Board of Fisheries, she said.

Brase plans to conduct an informal assessment of the pike population next spring.

“The plan is to get out there in a pair of hip waders or a canoe and walk or paddle around the weeds to see what we can find,” she said.