The reflecting pool in front of the Lincoln Memorial on the National Mall reopened a the end of August after a two year, $34 million reconstruction. It was the largest National Park Service project funded by President Barack Obama's economic stimulus package.

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Several weeks later, though, unsightly algae and scum has crept into the reflecting pool again. The algae can be seen at one end of the reflecting pool, almost completely covering the surface of the water.

“Looks like there's a fluffy, kinda cloudlike substance on the water, like it's green,” says Freya Newton, from Australia. “It's not very nice.”

Before the renovation, the pool had stagnant water in it and had begun to leak and sink into the land.

Now, however, the pool has been re-engineered with a circulation and filtration system. Instead of using city drinking water, it draws river water from the nearby Tidal Basin, which will save 20 million gallons of drinking water each year.

But that’s where the problems stem from. The Park Service says the Tidal Basin water isn’t chemically treated. Instead, it’s treated with ozone. The level of ozone, however, needs to be adjusted to prevent the algae from forming.

In the short term, Park Service staffers are trying to skim algae from the surface. In the long term, it is working to improve the filtration system to prevent further algae from growing.

National Park Service Spokesperson Carol Johnson says it's a new and complex system and they just need to fine-tune it.

“Nobody's ever done this before, so coming in from the Tidal Basin, we have to tweak it, make sure we have enough ozone, and we're pretty confident we've got it right now,” she says. “It's just going to take some time to get rid of what's there.”