Beaches open?

Hi, I'm wondering if anyone knows if Shirahama beach in Izu is still open. My friend said Okinawan beaches closed, while Enoshima beaches are still open, but I'm struggling to find info on the situation in Izu.

Shimoda's beaches are open, including Shirahama:
http://shimoda-city.info/
(scroll down for details on all of the city's beaches)

Am i correct that unless the coastal area is not a harbour or otherwise closed private property then in Japan the term "closed beach" means de-jure, that nobody isn't going to rescue you should you have trouble while swimming? And the sign in whatever form or language "Do not swim here!" is for your own safety and means that it is not illegal to walk near the coast and to go only knee deep in the water to tick the box "i am inside the Pacific ocean!"?

I have enjoyed the waves and ocean water in both Shirahamas (one near Shimoda and one in Kansai region) in mid april. Both were probably offically closed, but otherwise no issues. Of course, i went inside slowly and only as far as water level was up my waist for security reasons.

BR,
Lauri