Louise Cardwell: This is picturesque reservoir close to Edinburgh in a fabulous Glen . You may or may not like to know that at the point where the Kirk burn flows into the reservoir there is the flooded ruin of the 13th century St Catherine's Chapel.
Park at Castlelaw Car Park off the A702 Edinburgh/Biggar road. You will then need to walk cross country on the pathway that heads West until you can take a path down to the road (no unauthorised vehicles permitted on the road) that runs along the side of the reservoir. There is a path approx 200m from the car park, you will then walk on the road to the reservoir, or you can walk around the edge of the Castlelaw Firing Range and cut down to the reservoir after approx 700m, I personally prefer the off road option offering the best views, and both walks are a similar distance. There are various access points into the water depending how far West you wish to walk. Alternatively this is a great swim to cool off if you cycle through the Pentlands from Balerno!
Although used by boat and shore anglers the loch is big enough for both you and them to be undisturbed, beware of the active casting of the shore anglers at the West end of the reservoir (there are signs warning of this for the pedestrians and cyclists).
This is a public water supply reservoir and all usual precautions and considerations relating to this should be taken.