A heap of rocks in Berowra Creek at the upstream entrance to Marramarra Creek; submerged at high tide. Shown as Pelican Island on a 1926 chart, also known as Pelican Reef. William Bradley’s 1789 chart of Broken Bay and the lower river shows three very small islands at the location of Ballast Island so there was a reef of some kind at this site. During the nineteenth century, sailing vessels would have dumped their ballast on this reef in order to avoid creating another navigational hazard. Vessels sailing from Sydney to the Hawkesbury carried rocks as ballast and these were then thrown overboard when cargo was to be loaded. A number of these ballast heaps may be seen along the shoreline almost as far upstream as Windsor.