There's a monument located near the outlet of a spring on the river bottom. A photo of the monument: https://www.ardeaprints.com/manatee-monument-king-spring-182...
I couldn't visit the monument-- I hadn't learned to SCUBA dive yet. My father, who was an underwater photography enthusiast, took photos of it. The next year we transferred the photos and 8mm movie footage he shot onto VHS for me to show to my 6th grade class. I can remember him reading the inscription for the tape in a very somber voice.
> "Life must become more than the wants and needs of humans. We are not on this earth alone. If the manatee goes into extinction because the needs of humans became more important then we will have taken another step backward toward our own demise. Extinction is forever and for all." - Dr. Harvey Barnett
I'd love to find that VHS. His picture is somewhere in the mess of slides I need to eventually scan.
I'd also love to back and swim with the manatees again. Apparently their populations are doing better, though they're still at risk.