About 80 ducklings have been found dead in the Lincoln Memorial Reflecting Pool since May 20, the National Park Service said Friday.

Necropsies performed by the U.S. Geological Survey's National Wildlife Health Center determined the cause of death was a parasite known to grow in snails living in the pool, the NPS said.

Crews will fully clean the pool by draining it Sunday and then will chemically treat it and scrub it. The pool should be refilled by June 19, the NPS said.

After the cleaning and treatment are complete, the NPS will continue to monitor the water quality of the pool, the agency said.

The parasites' effect on humans is limited to an allergic reaction, called "swimmer's itch," which is not contagious and rarely requires medical treatment.

The risk of a person being infected at the reflecting pool is extremely low, because contracting the parasite requires sustained contact, such as swimming, according to the NPS.