A kayak gets you into the parts of this place a boat cannot reach and a boat's engine would ruin anyway. The mangrove tunnels behind Marco are a few feet wide in places, roofed with prop roots and crowded with mullet, small snook and wading birds that will let a silent hull get remarkably close. Nothing with a propeller goes in there, which is the point.
The island is unusually well set up for it. Marco has protected water on three sides — the Marco River along the north, Collier Bay and Barfield Bay behind, the lagoon system at Tigertail on the Gulf side — plus the Rookery Bay estuary to the north and the Ten Thousand Islands starting immediately to the south and east. Most of it is shallow, most of it is sheltered, and almost all of it is paddleable by someone who has never done this before.
The two variables that decide your day are tide and wind, in that order, and neither is the one beginners expect. Tide first: mangrove tunnels and the shallow back creeks need water in them. On a rising or high tide they open into something like a green corridor. On a falling tide the same route drops you onto oyster bar with a long, cutting walk out, and oyster shell opens skin like a blade. Any guided trip on this island is scheduled around the tide table rather than around a convenient hour, and a rental outfit that does not ask you what time you plan to go is not paying attention.
Wind is the second. There is no surf to worry about here and very little current in open water, but the Gulf sea breeze fills in through late morning and a fifteen-knot afternoon breeze across an open bay turns a pleasant outbound leg into a genuinely hard return. The standard advice on this coast — paddle early, be off the open water by lunch — exists for that reason rather than for the heat.
Third, less romantically: insects. No-see-ums work the backwater at dawn and dusk from spring through autumn, and they are small enough to pass through mesh that stops mosquitoes. A still, warm evening in the mangroves is exactly the conditions they like. Bring repellent, or paddle the middle of the morning.
Everything else is straightforward. The water is warm most of the year, the wildlife is genuinely abundant, and a two-hour guided trip is one of the better value things on an island where most of what happens on the water costs a great deal more.
