In a meeting with the investigator, Mr Bennett admitted occasionally smoking cannabis at home, but never at work.
The admission was reported to the council, and on January 7 he was asked to undertake a drug test, due to his "safety-sensitive" role.
The result of the drug test, taken on January 7, was positive. Mt Bennett later told his employer he had last smoked cannabis on New Year's Eve.
Mr Bennett was issued with a final written warning and asked to undergo a drug and alcohol rehabilitation programme, which would involve taking three months of unpaid leave.
He could then return to work at the lower position of full-time lifeguard.
Mr Bennett objected to the offer, and after five weeks of negotiations, his employment was terminated.
In considering the claim for interim reinstatement, the ERA said it was strongly arguable that the drug-test didn't meet the council's own policy on reasonable cause, as there was no evidence Mr Bennett showed any sign of impairment at work.
It was ordered that he be reinstated with immediate effect until his claim has been determined by the authority.
He is to undertake alternative duties and a rehabilitation programme, but be paid the operations manager salary.
The unjustified dismissal claim is to be investigated by the authority in June.