AUBURN — Last summer’s fish-killing algae bloom has not returned to Lake Auburn this year, according to water quality officials.

“We hope it never happens again. But if it does, we want to be ahead of it,” said Water Quality Manager Mary Jane Dillingham. She’s in charge of water quality testing for the Auburn Water District and the Lewiston Water Department.

But Dillingham said that does not mean the problem is gone, or that water officials are sure what caused the algae bloom. The districts stepped up testing this summer in an effort to survey the lake’s condition.

They’ll do it again next summer, hopefully zeroing in on the culprits behind the bloom.

“We don’t know if it was watershed input that caused it or if it was phosphorous from the bottom,” Dillingham said. “All this data we are gathering now, all this graphing and data, will be very useful in the future. We can calculate how much phosphorous is available. We’ll be collecting just as much next year.

“We’ve always done this kind of testing,” Dillingham said. “We are just doing so much more.”

Water quality officials discovered more than 200 dead trout along the shore or floating close to the shore in mid-September 2012. They blamed the kill on high phosphorous levels in the lake that encourage common blue-green algae to grow.

As the algae grows and dies, it sinks into the lake, decaying and using up oxygen in the process. That starves the fish, such as trout, that prefer the cooler bottoms of the lake.

Engineers found both elevated phosphorous levels and evidence of waterside erosion at several points along Lake Auburn’s feeder tributaries. Those include Little Wilson Pond, the Basin and Townsend Brook.

In response, water officials stepped up testing at the lake. Before, Dillingham said they tested quality multiple times each week at the deepest part of the lake, looking for dissolved oxygen and visibility.

This summer, they’ve tested quality three times each week at that deep hole, then at another five places at various locations around the lake. Tests include water visibility and dissolved oxygen examinations, but also counts of different kinds of algae, algae-eating plankton and phosphorous testing.

“It’s a much bigger program than we’ve ever done,” she said.

Water officials have also worked with Bates College to install a solar-powered buoy in the lake that constantly checks oxygen levels in the water. That live testing data is available online, at http://v4.wqdata.com/webdblink/hewing.php.

This summer’s tests show a healthy lake that seems to be recovering from last summer’s algae bloom. Visibility levels this year have been much improved compared to 2012 and 2011. Officials have not had to treat the water with copper sulfate algaecide.

The testing will continue, she said.

“When we are done, we should have a better picture of where in the watershed phosphorous is coming from and what it looks like in our lake, as well as what kinds of algae populations live there,” she said.

A final report, with suggestions, is due from water engineers in December.

staylor@sunjournal.com