Depending on mast height/tides, you may not be able to go further upstream than the railway bridge. No matter, the area has still got plenty of top places to stay at.
All down Cowan Creek there are little bays with public moorings in them. You're entitled to pick one up and stay for 24 hours. They can be hard to get hold of on some weekends but mid week you should have no problems. They are marked on the Maritime maps so check it out...
www.rms.nsw.gov.au/maritime/index.html Any of those spots is magic.
Right down the end is Akuna Bay which has D'Albora Marina. Never used it and suspect it could be a tad pricey but it'd be worth asking. There's Cottage Point and Brooklyn also have marinas and services. The Brooklyn marina does a nice fish 'n chip.
Over in Pittwater, the best place to stay is often the Basin (but can be exposed in a NE breeze and be prepared to be stung for a NPWS fee if staying overnight). Right down the end the RPAYC will let you use their marina, club and all facilities for a small fee (a mate did it for I think around $10).
