The 66-year-old Scotsman known as Jock or Jocka, had been visiting friends at the reservoir on Saturday night and was on his way back to his hut less than a kilometre away when his ute went over a steep bank and into the water.
"We're all in total shock. You don't think it will happen to one of our own," Fred McKnight, of Poolburn said.
Mr McKnight said Mr Williams, who was a carpenter by trade, had moved to Poolburn 19 years ago and one of the first things he did in the area was to help rebuild the Poolburn Hotel.
Though retired, Mr Williams continued to work as a handyman in the area including doing maintenance for the gun club where he was an honorary member.
He was a keen duck shooter and fisherman and would spend as much time as possible up at his fishing hut at the reservoir.
Mr McKnight described him as a "real character", a "story teller" and "just an all round good guy".
He said Mr Williams was not married and had no children. He did have two sisters, who would be flying over from Scotland later this week.
Police are continuing investigations and have not ruled out alcohol as a factor but the incident has been referred to the coroner.
