Some regions in Germany sweltered as the mercury hit 39 degrees Celsius (102 F,) and the German Meteorological Office said the country's all-time record of 40.3 Celsius (104.5 Fahrenheit) could be topped Tuesday.
Rivers like the Rhine and the Elbe have soaked up so much heat that fish are beginning to suffocate.
In Hamburg, authorities collected almost five metric tons (11,000 pounds) of dead fish from ponds over the weekend, dpa reported. Firefighters have started pumping fresh water into some ponds and lakes in a bid to raise oxygen levels.
In Denmark, where the Meteorological Institute reported that the month of July has been the sunniest since they started recording data in 1920, sales of alcoholic beverages dropped in favor of non-alcoholic beers, sodas and white wine, the country's TV2 reported.