Certain parks lend themselves to overcrowding, de Blasio said.
"We can't let that happen and we have to limit the number of people going in," he said.
The mayor said more details would be announced on Friday, but added that some "experimentation" would likely be necessary.
Cooped up New Yorkers flocked to parks last weekend during the warm weather. Smaller crowds are likely this weekend because it is going to be substantially cooler.
Playgrounds around the city remain closed.
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