Русско-английский словарь пословиц и поговорок
ТИХИЕ ВОДЫ ГЛУБОКИ
A quiet person can have strong emotions. See Большая река течет спокойно (Б), Где река глубже, там она меньше шумит (Г)
Cf:The shallow brook warbles, while the still water is deep (Am.). Smooth waters run deep (Br.). The stiller the water, the deeper it runs (Br.). Still water flows (runs) deep (Am.). Still waters run deep (Am.,Br.). Waters that are deep don't babble as they flow (Br.). Where the river is deepest it makes least noise (Am.,Br.)