Experts said they feared the number of drownings could rise above 40 by the end of the month, compared to 26 last year for the whole of July.
“The nice weather means people are out swimming and boating, and they expose themselves to risks,” Anders Wernesten of the Swedish Life Saving Society told TT.
“It is not unlikely that we will reach 40 this year,” he added.
At least six people died in drownings on Friday and Saturday, the news agency said.
While much of Europe has been sizzling in a heatwave, Sweden, like the rest of Scandinavia, has been enjoying pleasant and warm temperatures round 25 to 30 degrees Celsius (77 to 86 degrees Fahrenheit) for several weeks.