The devastating toll was described as “hard to comprehend” by police, while First Minister NicolaSturgeon said it was “heartbreaking”.
Edina Olahova, 29, and her son Rana Haris Ali, nine, is reported to have died along with a family friend, Mohammad Asim Raza, 41, when they got into difficulty near Pulpit Rock in Loch Lomond, south of Ardlui, on Saturday evening. A seven-year-old boy is also fighting for his life.
That tragedy was the fourth such incident in Scotland’s waters in just over 24 hours.
Assistant Chief Constable Mark Williams, of Police Scotland, said the tragedies had “highlighted that
open water is very, very dangerous”.
Mr Williams said: "The number of deaths in open water this weekend is hard to comprehend and my thoughts are with the families and loved ones of those affected.
“The warm weather can make open water swimming and paddling very inviting but it is extremely dangerous, even for the most experienced swimmers or supervised children.
"The conditions can change very quickly and there are often hidden risks like deeper water and strongcurrents.
“The message I want to send to everyone is exercise extreme caution. It is better to keep a safe distance from water if possible.
“Tragically, this weekend has highlighted that open water is very, very dangerous.”
He urged people: “If you see someone in the water and distressed, call 999 immediately.
“Remember, you could get into difficulty yourself trying to help so please take care and seek help as soon as possible.”
The incident at Pulpit Rock sparked a huge response with Police Scotland, the Scottish Fire and Rescue Service, HM Coastguard and the Loch Lomond rescue boat all attending the scene.
Police Scotland said formal identification of the victims is yet to take place but relatives of the three casualties have been informed. A full report on the circumstances will be reported to the Procurator Fiscal at Dumbarton.
A Police Scotland statement following that incident said: “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 seven-year-old boy was taken by ambulance to the Royal Hospital for Children in Glasgow and is currently in intensive care.”
Devastating weekend toll
It brought to six the number of people who had drowned in Scotland in 24 hours.
An 11-year-old boy, named locally as Dean Irvine, was pulled from the water at the Alexander Hamilton Memorial Park in Stonehouse, Lanarkshire on Saturday afternoon.
Emergency services were alerted at about 4.30pm, but Police Scotland said the youngster died at the scene after he was recovered from the Avon Water.
A member of a children’s group Monday Club, based in Hillhouse, where Dean is believed to have lived, said described him as “an absolute treasure” with a “cheeky wee smile and adventurous and contagious laugh”.
Less than two hours after this incident, a 13-year-old boy’s body was recovered from the River Clyde at Hazelbank in Lanarkshire following concerns raised at around 5.55pm.
Formal identification has still to take place but the family of the schoolboy has been made aware.
Those incidents came a day after Connor Markward,16, from Glasgow, died in Loch Lomond. He got into difficulty in the water near the pier at Balloch Country Park on Friday, sparking a major search.
The First Minister said her thoughts with the families of those who have tragically drowned.
Responding to the deaths, Ms Sturgeon said: “This is heartbreaking - my thoughts and condolences are with the loved ones of those who have lost their lives in the water over the past couple of days.
“In Scotland, we have some of the most beautiful lochs and rivers in the world - but if swimming in them, please take care.”
Health Secretary Humza Yousaf said the news was “absolutely heartbreaking”.
The SNP MP urged the public to stay safe and to heed Police Scotland advice on taking care in lochs and rivers.
Heed the warnings
People across the UK have been warned to take extra care swimming in open water after dozens across the country drowned during recent hot weather.
The Royal Life Saving Society described this week's deaths as "devastating" and urged people to choose supervised spots to cool off.
Lee Heard, RLSS UK’s charity director, said: “Whilst we recognise how tempting it is to cool off in the waterways, they hide hazards that tragically take lives each year and we urge the public to use caution when entering the water, getting acclimatised to the water temperature before jumping in.
“The difference between the air temperature and water temperature can literally take your breath away; this is called cold water shock. It is silent, invisible and deadly. Water can also hide debris, strong currents and sudden changes in depth that can catch out even the strongest swimmers. The Royal Life Saving Society UK urge everyone to learn vital skills and knowledge to prevent future accidental drownings.”
A spokesperson at Scottish Fire and Rescue Service said: “We are urging everyone to take care around water. If you find yourself in trouble, stay calm, extend arms and legs and float on your back, shout for help. Make sure everyone is aware of the risks and please stay safe.”