A 16-year-old from Sheffield dies after going missing while swimming in open water at Rother Valley Country Park in Rotherham on Monday, according to reports. The teenager was in the lake when they got into difficulty and could not be found promptly. Emergency services and local responders search the area as part of the incident response. The accounts also report that the death comes amid a wider heatwave period in which multiple other open-water drownings are recorded. One outlet states that a total of 11 people die in open water during the same heatwave conditions, linking the deaths to dangerous swimming and high temperatures. The reports do not provide additional detail beyond the location, age, hometown, and general circumstances of the incident. No further confirmed information about the exact sequence of events, whether the swimmer entered designated areas, or any specific safety measures in place is included in the provided text.