Dunalastair Water lies at the approximate grid reference of NN697584 it has an area of 165 hectares, being 2.5 km long and 800 metres wide at its broadest point.

The reservoir is narrow at its head, taking the form of a slender wooded glen with the Dunalastair estate situated on the northern bank.

The dam itself is 65 metres wide and has two floodgates and several spillways due to the quantity of water which sometimes needs to be released Into the River Tummel.

The main purpose of the dam is to act as an intake which supplies water to an open 15 metre wide concrete aqueduct that runs to the south of the River Tummel.

There are some very large brown trout which inhabit the water and feed mainly at night.