Swimming with the manatees was an absolute highlight of our trip! Prior to booking, I did quite a bit of research to make sure we were choosing a company that had the manatees' welfare in mind. I definitely didn't want to contribute to animal harassment or wildlife exploitation. After our experience, I felt like this tour was conducted in a way that was mutually beneficial for both the people and the manatees.
First, it's important to understand that there is a very large area that is off limits to the boats and swimmers where manatees can rest undisturbed. So, the manatees that were in the area where we were swimming were there because they wanted to be, which was a great feeling. Before the swim, we were educated on what to do and what not to do, which is basically boiled down to: float passively and wait for them to approach you. Don't chase them, and don't be noisy or excitable. That will just drive them away.
The cold February morning of our visit, we swam with probably around 10 manatees, including a mom and baby. At no point did I feel like we were endangering or harassing the manatees. In fact, as soon as I quietly slipped into the water, I felt one gently hugging my legs! I couldn't believe it! Other interactions included one swimming right up to my face and mouthing my hand, another mouthed my husband's goatee (maybe it thought it was seaweed???) and a baby manatee swam within feet of my face and just looked at me for a while. They were extremely inquisitive and interactive. We never sought them out - they came to us. It was an amazing experience!
If I could offer any advice it would be:
Book the early morning tour when they are apparently more active.
Don't worry about whether you'll fit into the wetsuit, they offer all ranges of sizes and there are curtained dressing rooms for you to struggle putting it on in private.
Don't worry if you've never snorkeled before, we had a first-timer in our group and she had an outstanding time.
Do bring your own underwater camera - I wasn't too impressed by the pics provided by the guide (sorry) - the photos I attached are ones I took with my 10-year-old underwater digital camera.
The water is a little murkier than I expected but the experience was seriously amazing. Just do it!