The brazen theft meant club members and other people using the lake would have to be more cautious in the future, he said.
"It's not ideal but it is something that would be good if people realise not to take things for granted."
There were a lot of children in the club and members would have to be even more careful with the children's belongings when they were out on the water, he said.
During training, members normally left their keys in the shed, which was left unlocked but bolted on the outside as it was difficult to keep hold of keys when on the lake, Mr Rimene said.
The club would be tightening up on security and was considering installing a combination lock.
"We are going to have to really think about that ... that trust has gone."
Mr Rimene said he was unsure if his wedding ring, a symbol of a more than 20 years spent with his wife, would be covered by insurance.
His first wedding band had been stolen while he was swimming in the Waipoua River five years ago and the replacement ring, which was stolen on Saturday, had fallen into the lake several years ago, only to be found by his son's friend while swimming about a week later.
"It was pretty lucky, but obviously that luck has run out."
Senior Sergeant Mike Sutton confirmed police were investigating.
Anyone who might have seen anything suspicious should contact Masterton police or call Crimestoppers anonymously on 0800 555 111.
