A Coroner's blamed modifications to a boat which sunk in a Southland lake for the death of a young man.

Jason Burford drowned in North Mavora Lake in August 2013, after he and two friends added a motor which was too heavy and powerful for the boat.

Whilst in the middle of the cold, isolated lake the motor ripped off creating a hole and sinking the vessel.

The 19-year-old's two friends swam to shore, one running for almost an hour to find help, but Mr Burford's body was later found in the lake.

Coroner Richard McElrea says Maritime and Water Safety New Zealand must highlight this tragedy, where all three people could've died.