"all forms of water sports practiced on open waterways, including sailing, windsurfing, canoeing, rowing, kayaking, surfing, paddle-boarding and the use of privately-owned motorised craft (in line with the guidance issued by the relevant navigation authority) are allowed. You can continue to use towpaths for walking, running and cycling, being mindful of other users and people living in boats along the water".
https://www.gov.uk/government/news/coronavirus-guidance-on-access-to-green-spaces?fbclid=IwAR14m70W-axMOSBDSzvN6nvOcl1xbPAGEoZ5i2bxAnVHfjK8b8-LbGC2afk
However, please ensure you check in advance that your chosen Marina, Slipway, boatyard, etc.. are operating in a Covid secure environment (Boris's words - not mine) and are open for business.
The following has been issued by Newhaven Marina:-
"There is now an ability to spend time outdoors, which we understand includes you being able to leave your home and visit your vessel at the marina either in isolation or with members of your own household only. Social distancing must be adhered to at all times, if passing people on the pontoons please use the finger pontoons as passing points to maintain a 2m distance from others. You may undertake inspections and maintenance on your vessel, but this is again subject to you social distancing throughout. In order that we maintain security throughout this process our marina gates remain closed and can only be accessed via a keypad. We are constantly adapting our working practices and cleaning of keypads and handles is now a part of the daily routine. Please however protect yourself by using disposable gloves or similar when touching such surfaces. Due to the high risk of close contact, the facilities building will remain closed until further notice, and in order to maintain social distancing the marina office door will remain closed, however our team are on site and able to provide services, so please call the marina office for assistance".