- - Thursday, August 15, 2013

A National Park Service cleanup crew began scooping 1,000 dead fish from the Constitution Gardens pond on the Mall on Thursday, a calamity caused by decomposing algae that depletes the oxygen in the water.

The fish kill — which created a terrible smell — happens periodically, Park Service spokeswoman Carol Johnson said.

Ms. Johnson said she does not know how many times the pond has had to be cleaned and restocked over the years, but she said fish deaths have been a “continuing problem” since the pond was built in 1976.

The shallow cement pond has no outlet to flush water, so when the temperature rises, algae grows on the bottom. When the temperature drops again, the algae dies and consumes the oxygen, suffocating the fish.

The Mall plans for reconstruction include a design competition for Constitution Gardens and the Washington Monument grounds that will address the pond’s ecological problems, officials said. Meanwhile, the pond will be cleaned out within the next few days, though the cleaning crew size is limited by Park Service budget cuts.

Workers will try to rebalance the pond’s ecology, but Ms. Johnson said she does not know whether the fish will be replenished before reconstruction.