A teenager has admitted to murdering beloved Canberra watersports stalwart Richard Dick Carter who was 82 years old.

The teen who can not be named because he was underage at the time made prehistoric monster sounds while he stomped on his head.

He was high on ice.

He also pleaded guilty to assaulting two other people in the horrific attack who were friends of Mr Carter.

The teen now faces the prospect of life behind bars.

The case returns to court on Thursday for a sentencing date to be set.