Ullswater is the second largest lake in the English Lake District.
And, many regard Ullswater as the most beautiful of the English lakes.
It is ~9 miles (14.5 Km) long and 0.75 miles (1.2 Km) wide with a maximum depth of ~60 metres (197 ft).
It is a typical Lake District narrow "ribbon lake" formed after the last ice age when three separate glaciers scooped out the valley floor. The deepened sections filled with meltwater and became a lake, after the glacier retreated.
The surrounding mountains give Ullswater the shape of a stretched 'Z'.
There are three distinct segments (or 'reaches') that wend their way through the surrounding hills.
Reference: Wikipedia