In Kanagawa prefecture, there is a project called Kanagawa Sea Project. One of the aims is to activate and stimulate the area through events relating to beach- & marine-life arranged with the help of local municipalities and NGOs. This page is a round up of all you need to know in order to enjoy these events!
Manazuru-Iwa Costal Area, Open-Water Swimming Tournament
Japan Coastline Acadamy
Hayama International Marina
Friendship Regatta 2018