Anyone up for a walk across the Central Park Reservoir?A rarely-seen divider that stretches across the center of the Manhattan watering hole was exposed this week as the city grapples with a historic rain shortage and drought.Dozens of birds were seen resting across the stone wall Thursday afternoon, taking advantage of a weir that is typically submerged beneath the Jaqueline Kennedy Onassis Reservoir.The sudden appearance isn’t the first time the dividing wall — a holdover from the reservoir’s days as New York City’s drinking source — has popped above water level, but it marks the first time it has emerged due to extreme weather.“The dividing weir has been visible from time to time over the last several years, typically when there is capital construction or repair work to be done on the reservoir,” Ted Timbers of the city Department of Protection, told The Post.The DEP said that the reservoir has lost enough water to drop two feet from its normal level in recent weeks, as a drought warning hovers over the Big Apple for the first time in 22 years.The 106-acre and roughly 40-foot deep reservoir — which typically holds more than one billion gallons of water — is supplied from upstate reservoirs, which have dropped below their own normal thresholds.“The Central Park Reservoir is no longer a part of the city’s drinking water supply system,” said Timbers.“However, when it was a part of the system it functioned with two basins, one on either side of the dividing weir, which is now visible. So what you are seeing now is actually how the reservoir historically looked, and how it was designed to look.”The reservoir, named for the former First Lady, was decommissioned in 1993 in part because of algae contamination concerns, as well as the upstate New York aqueduct expansion, according to the Central Park Conservancy.A significant swath of rainfall is expected to hit the Big Apple Thursday and Friday, raising hope for the end of the drought.The ex...