Silent Pool

Silent Pool is a spring-fed lake at the foot of the North Downs, about 6.5 kilometres east of Guildford in Surrey. It is managed together with the nearby Newlands Corner by the Surrey Wildlife Trust, within the privately owned Albury Estate. The outflow from Silent Pool runs into a second, adjacent, lake, Sherbourne Pond, created in the mid-seventeenth century. In turn the outflow from the Sherbourne Pond feeds the Sherbourne Brook, a tributary of the Tilling Bourne.
The Silent Pool Spring is the only major spring source in the 10.5-mile-long scarp slope of the North Downs between the Wey and Mole valleys. It discharges between 1 and 10 megalitres per day into Silent Pool; and the lake water exhibits a blue opalescence characteristic of chalk spring-fed ponds. In prolonged dry periods, Silent Pool has been known to dry up, although the lower Sherbourne Pond has not.

Wikipedia