Three people – a man, a woman and a child – have died at Loch Lomond after getting into difficulty in the water.
A seven-year-old boy is also fighting for his life in hospital after the incident on Saturday evening.
Police Scotland said they were called to a report of concerns for people in the water near Pulpit Rock, Loch Lomond, south of Ardlui.
A 41-year-old man, a 29-year-old woman and a nine-year-old boy were pronounced dead at the scene.
The seven-year-old boy was taken by ambulance to the Royal Hospital for Children in Glasgow.
A police statement said officers received an emergency call at about 6.40pm on Saturday.
It added: "A multi-agency operation took place and sadly three people were pronounced dead at the scene.
"Formal identification has still to take place but the family of a 41-year-old man, 29-year-old woman and nine-year-old boy have been made aware."
A report into the incident will be sent to the procurator fiscal.
Watch: Hottest day of the year in England and Wales
It brings the number of people who have died in Scotland after getting into difficulty in the water to five in just 24 hours.
An 11-year-old boy was pronounced dead at the scene after being found in the river at Alexander Hamilton Memorial Park in Stonehouse, South Lanarkshire, on Saturday afternoon.
About 24 hours earlier, a 16-year-old boy died in the water at Balloch Country Park at Loch Lomond.
Last weekend, six people drowned in lakes and rivers in England over the hottest weekend of the year.
Earlier this week, the Met Office issued its first-ever extreme heat warning.
Watch: Met Office warnings issued for thunderstorms and strong winds