Six members of the same family were in the water on July 22 when they got into difficulty, police said.
A seven-year-old boy remains in critical condition following an incident at West Mersea Beach which left his teenage cousin and her mother dead, police have said.
Sameeha Rahman, 15, her mother Shelina Rahman, 41, and seven-year-old Musa Ahmed were in the water along with three other family members – including two adults and one child – when they got into difficulty on July 22.
All family members subsequently made “significant efforts to help each other”, Essex Police said on Tuesday.
Sameeha and Shelina Rahman, from the Ilford area in east London, died, while Musa was flown to hospital where he remains in a critical condition.
A number of family members were also taken to hospital as a result of the incident and are recovering, the force added.
Detective Chief Inspector Al Pitcher, who leads the investigation, said: “We are continuing to support Shelina and Sameeha’s family through this extremely difficult time.
“They had been enjoying a family day at the beach together when this tragedy happened.
“We are working to establish the circumstances which led up to this incident and our inquiries are ongoing.
“We have spoken to a number of key witnesses and will continue to do so over the coming days and will work with partners including the fire service, local council, and coastguard.”
Chief Inspector Michelle Sparks, district commander for Colchester, thanked the local community for their response to the incident.
“There were members of the public who rushed to help the family and I want to thank them for their courage and selflessness,” she said.
“Since this tragic incident we have also seen an outpouring of support and sympathy.
“At times of tragedy you get to see how strong a community is, and we have a fantastic community on Mersea Island, and across the Colchester district.”
Essex Police previously said officers were called by the ambulance service at 5.35pm on July 22 after reports that several people had got into difficulty in the water near Seaview Avenue.
The East of England Ambulance Service said one patient was transported by air and three taken by road to hospital after the incident at Sea View Holiday Park.
Musa’s father Shahin Ahmed released a statement early on Monday in which he called for “a review of safety measures” at the site.
“I strongly agree with the calls from local residents for a review of safety measures at West Mersea Beach, including the provision of additional life-saving equipment and clear warning signage,” he said.
“While no action now can undo the pain we are suffering, we hope lessons can be learned to help prevent similar tragedies from happening in the future.”
