World Heritage Area designated by UNESCO, which stated that this status could be revoked if parts of the world heritage area were to be submerged. Activists also claim that the raising of the dam wall will give rise to additional developments downstream, which are currently not allowed to build on floodplains with a risk of a one-in-hundred-year flood. They also claim that any raising of the dam wall will be ineffective at flood mitigation, as the Warragamba River only contributes around 15% of water volume to the Hawkesbury-Nepean system. This issue has again been raised after the March 2021 Australian floods, with government ministers disagreeing on what needs to be done. Windsor Bridge Replacement Plans to replace the Windsor Bridge, and direct traffic through the historic Thompson Square caused significant community opposition culminating in the Community Action for Windsor Bridge (CAWB) movement. Despite this opposition, work on the replacement bridge was completed in May 2020. Third Crossing Plans for a third crossing at Navua Reserve in Yarramundi, and at North Richmond, 50 metres from the current Richmond Bridge Site are causing public opposition. Activists do not believe that these bridges will alleviate traffic, citing that a North Richmond and Richmond by-pass is required. River usage Navigation The Hawkesbury River is navigable from Windsor to the sea. There are no dams or locks on the river, and the effects of the tide are felt as far as Windsor. Whilst use of the river to carry farm produce and other goods has now largely been superseded by road transport, the river remains the only form of access to a significant number of isolated homes and communities. This is especially true in the lower reaches of the river, where the steep and rugged terrain inhibits road construction. One consequence of this is the operation of Australia's last riverboat postman, a river service that delivers mail to properties on the river between Brooklyn and Spencer. Sporting activities The Hawkesbury Canoe Classic, a 111 km canoe race, is held annually in October or November. The race starts at Windsor and finishes at Brooklyn. The Bridge to Bridge is a water ski race that is run in the opposite direction, from Dangar Island to Windsor. The Australian leg of the Red Bull Cliff Diving World Series takes place in Hawkesbury. Windsor and also Dargle ski park on the Hawkesbury river each year hold a Circuit Boat