The National Park Service announced it will drain and clean the Lincoln Memorial Reflecting Pool, after a water-borne parasite killed approximately 80 ducks there since May 20.

The service said Friday that postmortem examinations done on the ducks by the U.S. Geological Survey's National Wildlife Health Center suggested that their deaths were caused by "high levels of parasites that develop and grow in snails that live in the pool." Chemical treatments alone aren't sufficient to reduce the parasite and snail population, it said, so the service needs to drain and clean the pool.

In addition to killing ducks, the parasite - known as a schistosome - can cause swimmer's itch in humans, which is also called cercarial dermatitis.The CDC explains that the microscopic parasites "are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans). While the parasite's preferred host is the specific bird or mammal, if the parasite comes into contact with a swimmer, it burrows into the skin causing an allergic reaction and rash."

The risk of people contracting the parasite at the reflecting pool is "extremely low," says the Park Service, because you need sustained contact with affected water — and swimming in the pool has never been allowed. (Though it's been done.)

The draining will begin Sunday and the Park Service hopes to reopen the pool on June 19.

In 2012, the Reflecting Pool was completely rebuilt with water conservation features. The bottom of the pool was also tinted to make it more reflective.

According to the site Histories of the National Mall, the District of Columbia operated three small whites-only public pools near the Washington Monument in the mid-1920s and early '30s, which were demolished in 1935.

The site says that starting in the 1880s, there were segregated swimming areas near the Mall in the Tidal Basin: "In 1914, Congress voted to create an official beach on the Tidal Basin for white patrons. African Americans swam nearby in a segregated area that never received funding or buildings. Facing increased criticism from black leaders and concerns that the water was polluted, Congress voted to ban swimming in the Tidal Basin in 1925."

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