Rome, August 7 - You know it's hot in Italy when even the fish in Venice's lagoon are suffering. As average temperatures persist as high as 40 degrees C in parts of the peninsula, damage was feared to crops and gardens, to say nothing of health risks to the young and old. Even the fish were reportedly showing signs of heat strain. Venice city councillors called on citizens Wednesday to keep an eye out for dead fish as hot weather threatened to kill fish and rot seaweed in the lagoon around the iconic city. Environment commissioner Gianfranco Bettin appealed for residents to alert the authorities at the first sign of rotting fish. Meanwhile, some of the hottest conditions were reported in the Emilia-Romagna region of the central Italy, as well as in the South as weather system Styx continued to make itself felt. At least 17 cities were placed under serious health warnings because of the heat, with vulnerable senior citizens and children as well as those with chronic health conditions said to be at the greatest risk. Consumer group Codacons said that city emergency rooms everywhere from Milan to Rimini, Perugia, Verona, Padova to Pescara were faced with significantly high numbers of visits from people suffering from the heat. However, weather watchers said a storm system set to erupt by the weekend could bring some relief from the summer's third major heat wave. Unfortunately, that eruption will mean some "violent" thunderstorms in Italy's northwest areas, likely as early as Thursday or possibly Friday, said Antonio Sano, director of website ilmeteo.it. And that could even bring hail and tornadoes to some parts of Italy, he warned. Temperatures should ease by at least a few degrees through the centre and south of the country so that by Saturday, long-suffering visitors residents should feel "a real change," he said. Warm weather will continue next week but with slightly less blistering heat, according to the experts.