The action by local authorities came too late for the mother of Saran Srisongkram, whose lifeless body was pulled from the sluice between the lake and the seaside pond last weekend.
Yesterday she visited the scene with monks to bless her son's spirit.
The boy's life support was turned off at Vachira Phuket Hospital in Phuket City where doctors persuaded his family that he was not going to survive.
Children at the section of Nai Harn beach require constant adult supervision and the local Rawai council has undertaken to provide a lifeguard at times when holidaying families are most likely to be there.
New signs have been erected that warn of the dangers in three languages.
The lifeguards at Phuket's beaches guard the sands but not this corner of Nai Harn.
In any case, all 13 of Phuket's most popular tourist beaches are unguarded because of a dispute that arises almost every year when the lifeguards' role is put out to tender by the Phuket Provincial Administrative Organisation.
Managers at the Phuket Lifeguard Service say an agreement is likely to take several weeks yet, possibly leaving Phuket's beaches unguarded during the onset of the monsoon season, the most dangerous time of the year.