The Hawkesbury River, known locally as Deerubbin, is a significant coastal estuary forming the northern boundary of Hornsby Shire. It is a complex, winding saltwater system where freshwater from inland creeks mixes with the ocean, characterized by dynamic tidal flows and fluctuating salinity. The river offers a diverse paddling environment, linking inland landscapes with marine habitats. Key access points for paddlers include the village of Wisemans Ferry, which features a modern, three-lane public boat ramp with a pontoon, a large car park, and amenities. Brooklyn, another suburb on the southern bank, also provides convenient waterfront access near the Hawkesbury River railway station. The river is exposed to wind and open water conditions, particularly in its broader sections near Broken Bay, where paddlers can encounter challenging waves and headwinds. Significant boat traffic, including water skiing and houseboats, is noted, especially in summer around Wisemans Ferry. The area is a hub for recreational boating, so paddlers must remain vigilant. The scenery is dominated by sandstone cliffs and bushland, with the river flowing past holiday homes, marinas, and through national parks like Marramarra and Ku-ring-gai Chase. Wildlife is diverse, ranging from Wedge-tailed Eagles and White-bellied Sea Eagles to marine species like White's Seahorse. The overall vibe is a mix of active recreation and relaxed village atmosphere, with facilities like cafes, picnic areas, and playgrounds found at towns along the shore. Kayak and paddleboard rentals are available from operators in Brooklyn. Paddlers should be mindful that stormwater runoff from the catchment can impact water quality, and the estuary plays a crucial role in filtering pollutants. The river's geography includes numerous inlets and creeks, such as Berowra Creek and Mooney Mooney, offering sheltered exploration away from the main channel.