He said he and the harbourmaster were amazed they had not seen more accidents from the amount of "stupidity" they had seen around Rotorua.
"I think it's just a matter of luck."
People needed to be observant and learn basic boating rules, such as doing a day skipper's course, he said.
Mr Grouby would like to see everybody have to do a compulsory day skipper's course and receive some sort of boating card - like a driver's licence - which meant they had learned the basics.
Bay of Plenty Regional Council senior maritime officer Ross Powell said to have had three drownings on Rotorua lakes this summer was an absolute tragedy.
"Unfortunately there is a misconception out there that it's safer on the lakes than the ocean. The reality is you are less buoyant and it's often colder.
"Lifejackets only work if they are worn and we can't emphasise enough the importance of not just carrying them but actually wearing them."
Water Safety New Zealand chief executive Jonty Mills said there needed to be a dramatic change in Kiwis' attitudes and behaviour around water, and a shift in how water safety was perceived and funded.
"As a country, we have to ask ourselves whether it's okay to have one of the highest drowning death tolls in the developed world.
"If not, then we need to do something about it with every Kiwi taking personal responsibility."
Mr Mills said industry surveys, campaigns and research showed water safety messages were reaching their target audiences, but behaviour was not changing.
"It reflects the complex nature of the problem we face. In terms of water-based activities, the landscape is changing.
"We have increased immigration, an ageing population and increased tourism all adding to the complexity of the problem."
Mr Mills said a rethink was needed of how we approached and funded water safety.
"The water safety sector relies predominantly on non-government funding and a volunteer base. While demand on the sector is growing rapidly the pool of funding isn't."
Mr Mills said the sector needed to attract more funding and while more government support would be welcome, funding alone would not solve the problem.
"We need a culture change around water, similar to the wearing of seatbelts and drink driving."
Rotorua drownings 2017
- Auckland man Colin McCormick, 48, went missing on Lake Rotoiti on January 4. His - body was found on January 11.
- Rotorua man Shilo Paul, 31, drowned after falling out of his kayak on Lake Rotorua on January 17.
- Man in his 60s went missing while water skiing on Sunday on Lake Rotoiti. His body was recovered on Tuesday.
Top Boating Rules:
- As the boat driver, keep a constant lookout
- Obey your five-knot rules
- Take two forms of communication
- Wear lifejackets when moving
- Make sure your boat or water vessel is well maintained
Source: Coastguard Rotorua
