AUBURN — Cold weather could be the only thing to interrupt a fish-killing algae bloom in Lake Auburn, according to water officials.

State wildlife and local water quality officials began tracking the algae bloom last week, according to John Storer, superintendent of the Auburn Water District.

It’s not a threat to drinking water quality but could harm Auburn’s habitat for lake trout.

“Lake Auburn is a significant lake trout and salmon fishery in Southern Maine,” said Francis Brautigam, regional fisheries biologist for the Maine Department of Inland Fisheries. “These changes, if they persist, will potentially eliminate our ability to manage for lake trout there.”

Warmer water temperatures combined with shore erosion are encouraging the bloom and it won’t go away until temperatures in the lake dip later this fall.

“As an engineer, I wish there was an immediate man-made correcting measure,” Storer said. “I don’t think there’s a magic bullet here, just a long, slow process to correct this.”

Brautigam said higher phosphorous levels in runoff typically feed algae, which collects in the warmer upper layers of lakes and ponds. The algae die, and bacteria eat it as they sink to the lower, colder water levels. Those bacteria use up the available oxygen in the water, leaving little behind for the lake trout that prefer deep, cold waters. The fish suffocate in the water.

“You have two layers in a lake, the upper layers where you have wind mixing,” Brautigam said. “Those waters are usually always oxygenated. Then you have layers in the lower part that don’t mix with the upper part because of the temperature. So the only time you get new oxygen in the deeper water is in the spring and the fall, when the whole lake turns over.”

Storer said water district employees noticed five lake trout in distress over the deepest part of the lake on Thursday. They found more fish on Friday and notified state wildlife officials.

Nine dead fish were discovered Friday, five more on Saturday, none on Sunday and 21 on Monday. Storer said nine dead fish were discovered floating in the lake Tuesday.

Storer said dissolved oxygen levels in the lake were tested and found to be low this weekend.

Brautigam said shore erosion is usually the culprit behind algae blooms.

“What it generally reflects is an accumulation of nutrients in the water,” he said. “Water drains downhill and the more that builds up phosphorous in the sediment, the more it has available to grow algae.”

But the sudden increase in Lake Auburn is a surprise for biologists, however.

“I may not see another like it again in my career,” Brautigam said.

He has not seen tests performed on the lake but suspects this year’s weather conditions contributed to the problem.

“We had a very long growing season this year, a very long, hot summer,” he said. “We also had a lot of rain this spring which probably brought in a lot of nutrients. So all of that played out and resulted in a significant fish kill.”

Storer said the water district has tracked higher average water temperatures in the lake that could help encourage algae growth.

“What we have seen is that phosphorous has remained steady but that ice in, during the late fall and early winter, is coming later and later and the ice is gone much sooner than we have seen,” Storer said. “That’s giving us a longer period for the algae to grow.”

Storer said he is confident that the water district’s and the Lake Auburn Watershed Protection Commission’s forestry work along the lake have not made erosion worse.

“We have a forestry plan in place with the intent to keep the lake healthy in the long term,” he said. “We are quite confident that we have done everything right, as right as we can.”

staylor@sunjournal.com