The Lincoln Memorial Reflecting Pool Turned Green. Your Backyard Pool Doesn’t Have To.

The Lincoln Memorial Reflecting Pool has reopened, after a $14.2 million renovation that was completed last week as part of President Donald Trump’s preparations for America’s 250th anniversary.

During the renovation, leaks were repaired, a filtration system was upgraded, and, per the president’s request, the pool was painted blue. 

However, instead of a “flag blue” appearance, murky green water and algae greeted weekend visitors, which diminished the pool’s signature reflections. 

The National Park Service swiftly began cleanup to remove the algae as photos began circulating on social media. It has not said how long it will take to remove the algae and restore the pool’s appearance.

“The recent work done at the Lincoln Memorial is a great reminder that even the most iconic pools require consistent maintenance and occasional renovation to stay beautiful and functional,” says Jimmie Meece, brand president at America’s Swimming Pool Co. in Macon, GA.

If you’re lucky enough to have a pool at home, let this serve as a lesson that routine maintenance and proper filtration are well worth your time and money.

What causes algae growth in pools and how to stop it

“What you are seeing is residual algae from the supply lines," communications director Kate Martin said in a statement to CNN. The supply lines had been sitting dormant for eight weeks while construction was taking place, she explained.

This is part of the "normal startup process," according to Martin, and in speaking with experts, the same is true for backyard swimming pools, which can create the ideal environment for algae growth. 

Martin said that the National Park Service invested in “a state-of-the-art ozone nanobubbler filtration system” that is intended to keep algae out—but homeowners have far less daunting options.

Ineffective filtration, bad circulation, improper pH levels, and simply too much debris in the water can all cause algae to pop up in your pool.

However, low chlorine is often the main driver. 

To keep your pool from turning green, it’s your responsibility to maintain it regularly. 

The best way to do so is to monitor chlorine levels frequently. Realize they’re unstable as sunlight, rain, and even heavy pool use can significantly change them. And it's what keeps algae from growing in the first place. 

“Your goal should be to keep free chlorine—the active chlorine that sanitizes the water—between 1 and 3 parts per million. Test your levels every few days or more often after rain, heavy wind, or heavy pool use,” says John Uhle, founding partner and product expert at Discount Salt Pool in Waller, TX.

Don’t forget to check your pool filter—the cleaner it is, the better it will prevent your pool from turning green.

If you want to reduce the impact of sunlight on your chlorine, place a cover on top of your pool when you’re not using it. 

Also, if you know more people are going to use the pool than usual, test the water before and after swimming and be ready to add more chlorine if necessary. 

“Additionally, in case of rain and heavy wind, it's important to add chemicals based on water test results and remove debris using a skimmer after. Rain dilutes the chemicals, wind brings debris into the pool,” Uhle adds.

What to do if your pool is already green

It’s not uncommon for homeowners to uncover their pool and find green water after a long winter. 

If this happens to you, manual cleaning and shocking should do the trick. 

“Always start by physically cleaning debris using a skimmer and brushing the walls, floor, steps, and corners as algae forms on pool surfaces,” explains Uhle.

Once you remove the debris and brush the pool, test and balance the water before adding shock, which is a concentrated form of chlorine. It’s essentially a “deep clean” treatment you can buy at any home improvement store or pool retailer. 

“When you shock the pool, make sure the pump and filter are running, or the chlorine won’t circulate properly,” explains Uhle.

Also, let your green pool encourage you to be proactive. 

“Make sure the cover is in good condition, properly installed, and stays clean throughout the winter season to avoid green water. Also, test water levels at least once a month during the off-season and balance them as needed,” explains Meece.