A man who was being arrested in Ramsey on Saturday morning ran away from the police officers and jumped into the harbour.
Constable Saskia Baxter jumped in after him and swam out to rescue him.
As she reached him, Constable Mark Kerruish entered the water with a lifebelt and rope and they brought the man to shore.
The arrested man was taken to Noble’s Hospital for treatment.
Sergeant Vinny Lund said: ‘Without the bravery and quick thinking from both officers involved in the rescue, the outcome may been very different.
‘The man was out of his depth in the water.
‘To help us with our iinquiries, I would ask anyone who saw what happened or assisted officers to contact Ramsey police station on 812234.’
Both officers sustained minor injuries.
The man arrested was subsequently treated by the mental health service.