Part of the under-construction bridge on the Vaitarna river in Shahpur collapsed on Thursday killing three labourers on the spot. A fourth has been admitted to hospital and is in critical condition.
The incident took place around 10 am when the labourers had come in to work.
The Brihanmumbai Municipal Corporation (BMC) has undertaken the work on the dam as once completed, it will augment water supply to Mumbai.
The civic body is constructing two dams on the Vaitarna river, one is called Vaitarna and other is called the Middle Vaitarna.
The police have filed a case against the contractor, the engineers and BMC officers and the matter is being investigated, said inspector AB Patil from Mokhada police station.
Police said all labourers who died in the accident were residents of Madhya Pradesh and had been brought here by the labour contractor.
"We will check if the contractor had got the workers insured. We will also take the opinion of experts on the matter and will take action accordingly," Patil said.
When HT tried to contact Ajay Singh Pal, the contractor, he refused to comment on the issue and brusquely said nothing would happen to him.