AUBURN — Twin Cities water quality officials hope they don’t have to use an algaecide to prevent a fish-killing algae bloom this summer, but they want to be prepared.

Officials of the Lake Auburn Watershed Protection Commission plan to apply for permits that will allow them to put copper sulfate in Lake Auburn to halt a potential late-summer algae bloom. They will apply Monday to the Maine Department of Environmental Protection.

“This is a protective measure that we hope we don’t have to use,” said Kevin Gagne of the Lewiston Water District.

Officials hosted a public hearing for Lake Auburn neighbors and Twin Cities residents in Auburn Hall on Wednesday night. The lake is the water supply for Lewiston and Auburn.

Auburn Water District Engineer Sid Hazelton said he plans to meet with DEP officials Thursday to discuss the applications for the necessary permits.

Water-quality officials discovered more than 200 dead trout along the shoreline or floating close to shore in mid-September. They blamed the kill on high phosphorus levels, which 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. Fish such as trout, which prefer the cooler bottom of the lake, become deprived of oxygen.

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

Copper sulfate is an algaecide used to treat algae blooms in swimming pools and aquariums. It was one of the options discussed last month when the watershed group released results of its study of the fish kill.

Dr. Ken Wagner of Water Resource Services said the cities don’t want to use the algaecide.

“We are putting copper compounds in the water to kill algae,” Wagner said. “We hope to do it in a way that does not threaten any other aquatic resources, and we are quite sure there is no risk to people. But anything represents a risk, and we would prefer not to do it. But the alternative is to risk public safety by not treating the algae.”

The plan calls for water officials to monitor the conditions in the lake. The algaecide would be put in an area around the water district’s intake pipe — about 570 acres in the southern end of the lake — as soon as the algae growth is first noted. It should interrupt the growth cycle early, keeping it from killing fish.

It will be a single-year solution. Water officials are investigating ways to aerate the lake or kill algae in the long term, Wagner said.

“Nobody is suggesting that algaecide application is a long-term solution to the problem,” Wagner said. “It’s a stop-gap, interim measure to get us through, if we need it, until something else can be done.”

He said the application would use about 0.1 milligrams of copper sulfate per liter. Federal drinking standards stipulate that copper sulfate levels should stay below 1.3 milligrams per liter, so the Lake Auburn application should be safe.

Even so, the district would use drinking water from city reservoirs during treatment, Auburn Water District Superintendent John Storer said.

Lake Auburn’s most immediate neighbors who use their own intake pipes to get water from Lake Auburn said they were concerned.

“The drinking water is one concern,” said Barry Fraser of Church Street. “There is a risk here. It says it can be taken in through the skin, so how can I tell my wife she can take two showers a day and not risk concentrations that are dangerous?”

Storer said the district would work to test levels around private water intakes during treatment and would provide bottled water to affected homes.

staylor@sunjournal.com