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.
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A passer-by spotted the black and tan coloured snake in Hersham.
Police investigating the sexual assault of a 12-year-old girl at a swimming pool have issued an e-fit image of a man they want to trace.
Nazanin Zaghari-Ratcliffe was detained at Tehran Airport while visiting family in Iran with her baby daughter, Gabriella, in April 2016.