The black flies and mosquitoes were so thick he gave up on sketching and set out to go fishing alone one Sunday in Algonquin Park.
Tom Thomson's canoe was found floating upside down a few hours later.
His bloated body surfaced in Canoe Lake the next week – shrouded in a mystery still not laid to rest more than 90 years later.
How did the famous Toronto painter die on July 8, 1917: was it by accident, suicide or murder?
Who found his body?
Where are his remains buried?
These questions are explored in one of three new sections of Great Unsolved Mysteries in Canadian History, an educational website launched by the University of Victoria in 1997.
"It, for me, was just a compelling story," said project research director Gregory Klages, a graduate student in the joint communication and culture program at York and Ryerson Universities.
"It had all the great makings of a great mystery: a suspicious death, accusations of murder, suicide, accidental death, a question about where Thomson's body was buried.
"There just seemed to be so many questions."
Visitors to the site – called Death on a Painted Lake: the Tom Thomson Tragedy – are encouraged to tackle these questions themselves by combing through primary sources such as letters, journal entries and newspaper reports and draw their own conclusions about his life and death.
They will explore a young country grappling with its first great war and a landscape marred by the logging industry.
They will meet a cast of characters including his family, park residents turned murder suspects long after the fact, fellow artists like Group of Seven founder A.Y. Jackson and the various people – including journalist Roy MacGregor – who have investigated the story of his death.
"Growing up in a rural high school, we didn't have the opportunity to go to museums, to go to art galleries, to handle these primary documents," said Klages.
"Something like this site would have been tremendously useful.
"It's to allow students, on the one hand, to get access to the primary documents, to learn how to handle them [by] themselves responsibly as historians, as critical thinkers, and also by handling these primary documents, to make some decisions for themselves about what might have happened," he said, adding they will be learning about Canadian history and art as they go along.
The site also offers contemporary interpretations of the evidence, including a report by Chief Forensic Pathologist of Ontario Michael Pollanen.
Pollanen concluded the coroner at the time – who never examined the body – was wrong to agree with a doctor's opinion that the cause of Thomson's death was accidental drowning.
Based on the available evidence, Pollanen concluded, the cause of death is unknown.