I snorkel in the 4 foot deep pool in my back yard, and let me tell you, you really need to know what you're doing or it can result in disaster. Its a miraculous world teaming with beauty (my daughter), danger (my son), and wildlife (diving beetles). Invest in good gear and take care of it.

OK, so I got certified back in my younger days, but family life and other priorities haven't allowed me to go diving in many years.

My advice would be to find SCUBA clubs in your area - often associated with SCUBA gear stores - and seek their advice. NYC has to have lots of them. I would think that the small stores are going to cost more than on-line, but they can also offer some good advice.

Also check out http://www.scuba-forum.com and http://www.scubaboard.com