Those strolling around on the trail by Lake Agnes in Alexandria Tuesday may have done a few double takes. A big barge-like pontoon with five large cylinders was floating around the lake.

And there were big tanker trucks, hoses and other equipment set up near the shoreline.

It was all part of an effort to make the water cleaner by treating the lake with a chemical compound, aluminum sulfate, commonly referred to as alum.

The Alexandria Lake Area Sanitary District accepted a $300,000 bid last month from HAB Aquatic Solutions to treat the lake with 129,424 gallons of alum in two applications, one this fall and another in the fall of 2022.

The sanitary district is trying to reduce the amount of phosphorus, which spurs the growth of algae. It’s exploring ways to remove invasive carp, which stir up phosphorus, and is using alum to bind to the phosphorus and sink it to the bottom of the lake.

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Homeowners around the lake were notified about the treatment, according to ALASD Plant Superintendent Scot Spranger, who was observing the operation Tuesday morning.

Spranger said that as soon as the alum was applied, he could see the water start to clear up. He added that ALASD will do some testing to see how effective the treatment was.