We stayed in one of the local hotels on Marco Island (Marriott) and used their beach hut to find tickets on the Calusa Spirit.
Listed as a 2.5 hour tour, it was more like 3 hours, every minute great. The EcoTour is a fun way for kids and adults to learn about the environment and native species of Marco Island and the saltwater edge of the Everglades.
Mangrove thickets with sea birds of all sorts -- we loved the pelicans' graceful soaring across the water and PLOP! into it. Some of the folks on our boat saw a big sea turtle. We looked but missed there were no manatees to be found. We saw lots of bottlenose dolphin action: playing in the wake of our boat, chasing fish into the sea wall and feeding, watching us on our boat.
The tour includes an hour-long stop on an uninhabited island to collect shells and peep at a historically-interesting now-deserted dome house that's falling into the sea. We even saw some loggerhead turtle nests! So much to enjoy and talk about with our kids for days to come.
The Captain and tour guide were knowledgeable and fun.
Be aware: there is no dock access to this boat. You must wade out to it and climb a ladder. Depending on the tide, that may mean wading into waist-deep water (for a grown-up). Dress appropriately, pack lightly, and prepare to help/ carry the kids.
Sunblock a must. No need for Dramamine.