The deceased, who are believed to be a man in his 40s and a woman in her 60s, were recovered from the lake, following an incident involving a capsized boat on the lake on Wednesday. No other boats were involved in the incident.
Police say they are currently awaiting formal identification of the deceased to be completed.
A third person, a woman in her 50s, remains in a critical condition at Derriford Hospital in Plymouth.
Devon & Cornwall Police is now in close liaison with both the MAIB and HM Coroner as what is expected to be a complex investigation is progressed.
Superintendent Toby Davies, from Devon & Cornwall Police, said: “This has been a tragic incident in which two people have lost their lives.
“We continue to support all of the families involved with the deployment of specialist family liaison officers and our thoughts remain with those families at this difficult time.
“The parallel investigations will look at the circumstances surrounding the incident with the MAIB in addition identifying ways to prevent a similar incident occurring in the future.
“These investigations have already seen liaison with HM Coroner and we would expect this to progress further during the next week.”