The coroner's inquest into the death of RCMP Constable Michael Potvin opened today in Whitehorse with testimony from an eyewitness.

Potvin drowned in the Stewart River at Mayo in mid July, 2010, when the RCMP boat he was in capsized.

Mayo resident Joanne Buyck told the inquest she was in a cafe near a boat launch in the community when the incident occurred.

She says a local man called for help and her son ran to the riverbank.

Buyck followed a short time later.

She says she saw Potvin swimming for shore and another officer hanging onto the boat.

In the meantime, a group of local men were putting a boat in the water.

Buyck says Potvin was swimming well and she thought he was going to make it when suddenly his head and arms shot straight up and he disappeared.

Buyck says she went back to the cafe and called Whitehorse RCMP.

Another witness, David Lucas, said Potvin yelled to others to help his partner, who was still clinging to the boat, before Potvin disappeared into the water.

The inquest continues.