I was wondering if there were any good locations in New York (Either New York City or Long Island) where I can find quarry mud or tidal mud. Any suggestions?

I've been on the same search myself and within the last year or so, by riding the train, discovered that these coves on the north shore of western long island have tidal mud. However, I'm not sure how safe they are. In fact, the western most of the three specifically has a sign saying basically that it's toxic. There's actually an article about it here https://ny.curbed.com/2016/6/9/11891372/nyc-parks-alley-creek-queens-photo-essay
I'm not sure about the other two. I've never gone to go look out of fear of being seen. Considering how close they are, it makes me wary