The safety group Rospa's report on the western beach pool on Concord Beach, Canvey Island, says it presents "unacceptably high" risks to users.
It says the poured concrete floor of the pool is an "extremely hazardous" surface for young children to walk on.
Castle Point Council called the report flawed but is still closing the pool.
It said it would seek further safety advice about the pool's future.
The Rospa report was commissioned by independent councillor Colin Letchford who said he was concerned about the work undertaken to create the pool in 2000.
"The sandy bottom was replaced with concrete," he said. "Since then there have been a number of accidents."
The report also claimed the pool wall is "very hazardous to walk on" with an "extremely slippery surface".
It adds: "Despite well-positioned signage warning of the risks of going on the wall, these warnings are reported to be frequently ignored.
"In view of the issues identified in this report the risks to users are unacceptably high. Rospa strongly recommend that the facility is closed [until work to make it safer is carried out]."
A spokesman for Castle Point Council said: "The Rospa report was commissioned by councillor Colin Letchford who has no authority to act on behalf of the council.
"The report was compiled without the involvement of the council officers who are responsible for the operation and management of the facility or sight of the council's risk assessment for the pool.
"As such the council believes the report is fundamentally flawed and has raised its concerns about the inspection methodology and accuracy of the report with Rospa. Given the report's conclusions the council has no alternative but to close the pool pending further safety advice."
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