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Algae Prevention

Hot and dry summers, such as what Aurora experienced in 2020, can lead to potential algae overgrowth, including harmful blue-green algae. To get ahead of this, Aurora Water applied hydrogen peroxide and aluminum sulfate (alum) to the reservoir Sept. 28 through Oct. 9. as a preventive measure. Quincy reopened for all uses, including boating, fishing and wading, on Saturday, Oct. 10. 

What is blue-green algae?

Blue-green algae are naturally occurring cyanobacteria which, in the right conditions, can bloom out of control. Algal blooms occur throughout Colorado and the U.S. when temperatures and nutrients, such as phosphorous, can encourage algae overgrowth. Algal blooms are bright green and often look like paint has been spilled. It can cause foul odors, and when blue-green algae are present, can be harmful to people and animals.

How does hydrogen peroxide work? 

Hydrogen peroxide is an effective antiseptic that can greatly reduce the amount of blue-green algae living in the water. It is a safe reservoir management tool commonly used to control algae growth and improve the overall ecological health of reservoirs. This method of algae control has been used throughout the U.S. for the last 20 years and is safe for people, fish, plants and animals. Using hydrogen peroxide for water treatment leaves no chemical residue; it breaks down into separate hydrogen and oxygen atoms that simply become part of the water.

Why is it necessary to also use alum?

The next step in minimizing the growth of harmful algal blooms will be applying alum. Alum starves algae of its food source by locking away the nutrient phosphorous. The treatment is expected to dramatically reduce algae growth and improve water clarity and quality. In other reservoirs, alum has been long acting and restricts the algae growth for five or more years.

Is alum safe?

The health and safety of Aurora Water customers is the top priority. Applying alum is a long-standing reservoir treatment used on water bodies throughout the U.S. and recognized as safe to human health and the environment. Alum is commonly used in drinking water treatment and is used at several of Aurora’s drinking facilities. Aurora Water regularly tests Quincy Reservoir.

What can the public expect to see after the treatments? 

Once these treatments are applied, the reservoir will have cleaner and clearer water, a healthier ecosystem and be and overall better recreational amenity.

Will this affect the drinking water?

Currently, water is not being drawn from Quincy Reservoir. Aurora's drinking water meets or exceeds State and Federal drinking water standards. Aurora Water conducts more than 80,000 sample tests system-wide to ensure safe and great-tasting drinking water is delivered to homes and businesses. All three of Aurora Water's water purification facilities have achieved the Phase IV “Excellence in Treatment” designation, the highest level awarded by the Partnership for Safe Water. Aurora Water is the only water provider in the country to earn this designation at three facilities. More information about Aurora's water quality can be found at

Does this mean that Quincy Reservoir will no longer need improvements?

Aurora Water and the city of Aurora's Parks, Recreation and Open Space have jointly started a comprehensive analysis of the long-term health of this drinking water source and recreational amenity. Updates and project information will be posted on this page. Check back for more information.

Questions? Email us at [email protected].

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