You can reach the Dam in many ways, by either taking the longer option from Cowan train station walking via Jerusalem Bay and finishing up a Brooklyn. Where you have Hawkesburry River railyway station to get a train back. Otherwise you can also just start from Brooklyn and walk approx 2 k's to the Dam and return back the same way.
Brooklyn offers some great Fish and Chips and a well deserved rest at the Anglers Arms before heading home.