Rowing Canada announced Spracklen's departure on its website. The sport's governing body merely said Spracklen will not return to his post, and did not describe his departure as either a firing or resignation.
"It's unfair," Laumann told the Canadian Press on Tuesday. "I'm fully supportive of Mike and his coaching style and I think it's a pretty major mistake on Rowing Canada's part to let Mike go."
No reasons were given, but Spracklen has had a fractious relationship and public spats with Rowing Canada for a number of years.
"Mike's a guy who speaks his mind," Laumann said. "He fights for the athletes. So if he thinks that the administrators and Rowing Canada are doing things that are not in the best interests of his athletes, he'll let them know."
Spracklen, a 75-year-old Marlow, England native, guided the men's eights team to a silver medal at the London Games, following up on gold in the men's eight in 1992, silver and bronze in 1996, and gold in the men's eight again in 2000 and 2008.
"That silver medal (from London), just to put that in perspective there were only two guys in that boat that had medalled before," Laumann said. "He took a relatively inexperienced group of men ... and was able to pull them together to create a silver-medal performance.
"I think it's pretty hard to argue he's not on top of his game when he's producing results."
He also helped Laumann earn a bronze medal in 1992, when she overcame a broken leg suffered in a freak accident 10 weeks before the Barcelona Games to step up to the podium. Spracklen mentored Laumann between 1990 and 1996, when she capped her career with a sliver medal in singles sculls.
She also won a bronze in double sculls in 1984 in Los Angeles.
"Mike's sort of been handed that label, that he's a divisive coach," Laumann said. "I don't believe that's true, it certainly wasn't true in 1992.
"He's a strong coach, he has strong opinions and sometimes other people don't agree with him. But I think Rowing Canada has created a situation that's augmented any divisiveness that was there in the first place."
Laumann said it was hard to argue with Spracklen's track record and he had at least two more Olympics in him.
"Mike's track record is unquestionable," Laumann said. "He has won more medals for this country than any other rowing coach, dare I say any other coach, that Canada has ever employed."
In a news release, Rowing Canada praised Spracklen and said he has left a "significant legacy."
"We thank Mike for his tremendous contributions to Canadian rowing, and we know he will be missed by many of the athletes he has worked with," said Rowing Canada high-performance director Peter Cookson. "Mike has left a significant legacy and we respect and celebrate his many achievements."
Rowing Canada said the performance director of the heavyweight men's program, based in Victoria, will be announced, along with other appointments at a later date.
Meanwhile, John Keogh was named the new performance director for the women's program, to be based in London, Ont. Al Morrow, a member of the Canadian Sports Hall of Fame and a multiple Olympic medal-winning coach, was appointed head of the men's lightweight men's program, which will also be based in Ontario.