Bushwalk down to the weir, then back up by a different route, with short walk along Comenarra Parkway to get back to start.

Make sure to go forwards on this walk the first time, because the exit from Lane Cove National Park is very hard to spot from Doncaster Avenue.

Note that Ramsay Avenue is a cul-de-sac, and doesn't actually connect with The Comenarra Parkway.  The entrance to Lane Cove National Park is near the top of the hill heading north-west along The Commenarra Parkway from Evans Street.

Steep climbs and a few soggy patches.  The western-most part of the walk has a large rock beside the path (at the top of the hill) which commands superb views of the valley. 

Many of the walks in the Lane Cove National Park become impassable with heavy rain, but this one seems to be ok in all weather.

Turn on Satellite mode and zoom close to see how accurate my path is compared to the photos.  Note that the hairpin turn at the southernmost part of the route feels like a double-back onto the same trail, but it really takes you up to Doncaster Avenue.  If you fail to make the full hairpin turn, you end up walking a steep hill to Wallalong Crescent, with a much longer walk back to your car.