Because water is densest at 4 degrees, the bottom of every (big enough) lake is that temperature. If they pumped warm water in at the bottom, it would rise beca

Because water is densest at 4 degrees, the bottom of every (big enough) lake is that temperature. If they pumped warm water in at the bottom, it would rise because it’s less dense. Regardless that lake is so huge, it would have negligible impact on the overall temperature.