Rescue teams have described the weekend when six people died in incidents on the water as “the worst in memory”.
A man, woman and boy died in Loch Lomond near Ardlui on Saturday evening.
It came hours after the death of an 11-year-old boy in a river near Stonehouse, South Lanarkshire.
The body of a 13-year-old boy was also recovered from the River Clyde near Lanark on Sunday, while a 16-year-old boy died near the pier at Balloch Country Park on Friday.
Deputy Assistant Chief Officer Alasdair Perry, from the Scottish Fire and Rescue Service, said: “This is the worst weekend in relation to incidents of this nature that I can remember.
“I’d like to offer my condolences, and those of everyone at the Scottish Fire and Rescue Service, to all those affected by this weekend’s tragic events.”
Police Scotland said three people – a 41-year-old man, a 29-year-old woman and nine-year-old boy – were pronounced dead at the scene. A seven-year-old boy was rescued and taken to hospital in Glasgow where he is now in intensive care.
Simon Jones, executive lead for water safety at the Loch Lomond and Trossachs National Park, said it has been a “very traumatic time” for staff involved in the search and rescue attempt.
He told the BBC’s Good Morning Scotland programme: “It has been a terrible week in the park, and of course across other parts of Scotland, with these tragic events. Our deepest sympathies go to the friends and families.
“We can’t remember a period like this. Many of our staff were closely involved and it has been very traumatic.
“It has been really challenging and sobering and has given us a lot of cause for reflection on how we move on from these events.”
Mr Jones said national park staff would continue to be pro-active in encouraging people to enjoy the “beautiful and iconic loch” safely.
He said: “Collectively, we all have to look at what more we can do – from understanding what the risks are if you are a visitor, through to the authorities about how we engage with people and what equipment is provided.
“Daily patrols already take place commonly throughout the loch.
“We all have a responsibility to make sure that we are aware of dangers and allow people to make active decisions about where water is safe and where it isn’t.”
Scotland’s health secretary, Humza Yousaf, said the country had been “rocked” by the series of deaths.
He said: “We in government are committed to do what we can to support those in our national parks to make our lochs and tourist hotspots as safe as possible.
“But at the moment all I can say is just what a tragedy this is.”
The Scottish Fire and Rescue Service has repeated its warning about the dangers of cold water shock in warm weather.
Deputy Assistant Chief Officer Alasdair Perry said: “When we look at the weather we’ve had this weekend, it’s sunny and very warm in most areas, but the temperature of the water can still be extremely cold.
“If somebody enters the water they can suffer from this physiological response called cold water shock and that impacts their ability to control their breathing, their strength can be affected and their ability to swim.
“This can affect anybody of any age and any fitness level.”