[1] It rises on Matlock Moor, flowing south through Cuckoostone Dale, under the A632, into Lumsdale, gathering the valley's waters—notably from Knabhall Brook, out of Tansley, itself dammed and supporting large mills.

Finally, it runs through control gates into the outside bend of a tight oxbow of the River Derwent, just beyond Hall Leys Park in Matlock.

From high on its dam wall, a still-visible metal pipe conducted water to the wheel of the adjacent, second mill, dating from 1850, and still functioning as a sawmill at the turn of the 20th century.

The power of Bentley Brook has carved an impressive series of waterfalls from the limestone, and has led to tragedy in the recent past.

On 10 December 1965, heavy rain caused major flooding in Derbyshire, leading to three fatalities, including a 58-year-old railway worker, George Ellis, who was found dead in Bentley Brook in Matlock, two days after he had last been seen attempting to cross a flooded car park bordering the Brook.