Police are continuing to search for two people following the incident on Roadford Lake near Okehampton on Wednesday.
Two people were removed from the water and taken to Derriford Hospital, Plymouth for treatment.
One person has been discharged but one person remained in hospital in a critical condition.
Roadford Lake Activity Centre was closed until further notice.
Four were rescued and two people remained missing as the search ended at nightfall at the 130ft deep lake – one of the biggest inland waterways in the South West.
The two other people were safely recovered from the water.
A spokesman for Devon and Cornwall police said: “Police remain at Roadford Lake in Lewdown, Okehampton, following an incident on Wednesday where a boat capsized in the water.
“Police-led searches have recommenced today Thursday and efforts continue to locate two missing people.
“Two people were removed from the water and taken to Derriford Hospital for treatment.
“One person has since been discharged and one person remains in hospital in a critical condition.
“Two other people were removed from the water and checked by ambulance teams before being discharged at the scene.
“We are supporting the families of all those involved.
“The lake will remain closed for public access for the foreseeable future and localised road closures remain in place at the activity centre to allow access for the relevant emergency services.”
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