NYC swimming pools are open and Brick Underground has a comprehensive guide that they have published. Lasker Pool in Central Park is worth mentioning and is an Olympic size pool with lots of space though the morning session is a little more tranquil than the afternoon. One of the best tips is that the water is very cold and best on a very hot day. Read their full post to learn about the most recent renovated pool in the system as well as what to bring with you and what not to bring.
For those of you bringing the little ones, Lasker makes you leave the strollers outside but will let you bring car seats in. There is an area for the littlest little ones with fountains as the general pool can be a little raucous at times. Also the water in that area is a little warmer. Happy Summer!