WASHINGTON (AP) — The National Park Service has once again drained the reflecting pool in front of the Lincoln Memorial in Washington to clean up an algae buildup that formed after a $34 million overhaul.

Park service spokesman Carol Johnson says the pool was drained and was being cleaned Thursday. It will remain empty for at least a week.

Algae and scum have been covering parts of the pool since it reopened. It had been closed for a two-year renovation and was reengineered to draw river water from the Tidal Basin instead of city drinking water. The system is supposed to filter and circulate the water to keep it cleaner than in the past.

The park service says the system that fills the pool is being recalibrated to neutralize nutrients that feed algae.

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