Thanks to everyone for their help. I've had a look at the aerial maps but not sure if it's doable as yet. There appears to be tracks but I don't know what they're like. A guide sounds good! Found what looks like a crossing on the east side of the reservoir but not sure of the track going through the plantation. Also, it looks like we could get across from the carpark up the top. I wonder if it's possible to walk close to the water's edge? Both farms are recommended as good fishing spots!