AUBURN — An effort to remove algae-producing phosphorus from Lake Auburn will begin July 10, when officials will apply a dose of aluminum sulfate to three-quarters of the lake.

Officials at the Auburn Water District and Lewiston Water Division detailed the plan in February, after the district came under scrutiny following an algal bloom late last summer that led to taste and odor issues in the water.

A news release July 3 from Superintendent Sid Hazelton said aluminum sulfate is widely used in drinking water treatment plants as a coagulant and in lakes to improve water quality.

In order to combat the increased presence of algae in the lake — due to phosphorus from stormwater runoff and higher average temperatures — the district has also applied algaecide to the lake in September 2018. Hazelton has repeatedly said that all drinking water standards were met “before, during, and after these events,” but the episode led to more calls for changes in protocol, including an argument led by Auburn Mayor Jason Levesque that the two cities should build a water filtration plant.

Because of historically clean water, the Auburn Water District receives a waiver of filtration that allows it to treat the water with ultraviolet light and other means without having to pay to filter it.

In the news release Wednesday, Hazelton said district officials, consultants and state officials “agreed that an (alum treatment) to Lake Auburn in 2019 was the best option to improve the quality of our drinking water.”

The district received its permit from the Maine Department of Environmental Protection in May.

According to Hazelton, phosphorus promotes algal growth and in this application, “the alum will bind the available phosphorus and sink it to the bottom of the lake. As an added benefit, some of the phosphorus that is present in the lake sediments will bind with the alum and not allow it to be released into the water column.”

He added, “Based upon similar projects that have been done here in Maine, we anticipate several years of improved water clarity that will ‘buy us time’ to implement additional watershed protection efforts that will limit the amount of phosphorus that is entering the lake.”

The project will be a one-time dose of 2 milligrams per liter over three-quarters of the lake. The application will occur over a three- to four-week period from a barge with a submerged diffuser bar.

“Due to the chemical nature of alum, and the fact that the concentration of this application will be very low, we do not anticipate any measurable impacts on fish or aquatic organisms,” he said, adding that an area without aluminum sulfate will be maintained around the drinking water intake during application.

The boat launch will be open during the treatment, he said.

“We will closely monitor and test the water before, during and after the application to assure we continue to meet all drinking water standards,” he said.