"The idea here is to put health and safety first," de Blasio said. "No one has to be reminded, we are the epicenter of this crisis."
The announcement comes two days after Governor Andrew Cuomo's announcement about the reopening of beaches in New York state for Memorial Day weekend.
Beaches in New Jersey, Connecticut and Delaware are also opening.
While walking on beaches are permitted with proper social distancing measures, the mayor said beaches will remain closed for swimming. NYPD and NYC Parks will increase their patrols in those areas.
De Blasio gave examples of some places opening up too quickly and seeing an uptick in cases.
"For whatever reason, (they) decided to reopen quickly, even though there wasn't a lot evidence that it was safe," he said.
De Blasio said the city will add fencing to control entry points, and access to beaches will be further restricted if social distancing or no-swim rules are not observed.
Opening later in the summer is contingent on further reduction of COVID-19 and resumption of non-essential activity and travel, the mayor added.
NYC Parks is training lifeguards to ensure staffing if the city decides to reopen beaches safely.
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