London Zoo says it believes Melati carried the cub outside, but keepers are unclear as to how the cub got into the pool.
Keepers are now reviewing the situation because it was not forseen that the mother would take the cub outside so early.
More top news
The move comes amid a motion of no confidence that was tabled against Labour leader Jeremy Corbyn.
Detectives investigating an assault in Newham have released CCTV footage in a bid to identify the two suspects who attacked a 23-year-old.
Concern is growing for the welfare of a 28-year-old woman who has not been seen for more than two weeks.