Why has Daming Lake in Jinan been silent until the snake sees the frog?

More scientifically, the water in Daming Lake is collected from Jinan spring, and the temperature of the spring is relatively low, while water snakes need higher water temperature to swim and croak on the water. There is also a saying that Emperor Qianlong won't let them disturb their tryst with Xia, so snakes in Daming Lake are not allowed to go out of the water and frogs can't sing.