If you are going strictly for the manatees, you will be very disappointed by going in July. Peak manatee season runs from November to early March. There are a few year round manatees, but they are very few and far between and finding them would be almost impossible. I put together a manatee trip every year for my scuba group and we go the 1st or 2nd weekend in December. We have actually had a couple years that we had issues finding manatees even during that time of year, and that’s with a local Charter (Bird’s Underwater) that knows where to find them. That being said, Crystal River is a very quaint little town and there is some decent diving in the area. Rainbow River drift dive at KP Hole is always fun. You can dive the cavern in King’s Bay and there are a few springs; Blue Grotto, Devil’s Den, Hudson Grotto, etc that are pretty local to the area.
Hope this helps a little bit..
Dale