Marco River Marina, 951 Bald Eagle Dr. (tel. 239/394-2502; www.marcoriver.com), is the center for boat rentals, fishing, and cruises. Operating from a booth on the marina's dock, Sunshine Tours (tel. 239/642-5415; www.sunshinetoursmarcoisland.com) will book offshore fishing charters and arrange back-bay fishing ($57 for adults, $47 for children 9 and under), shelling excursions to the small islands ($47 adults, $37 children 9 and under), sunset cruises ($26-$40 adults, $22-$25 children), and dinner cruises ($49-$52 per person). The back-bay fishing trips go at high tide, the shelling trips at low tide; call for the schedule and reservations.
SCUBAdventures, based at 845 Bald Eagle Dr., Olde Marco (tel. 239/389-7889; www.scubamarco.com), charges $75 to $95 for two-tank dives, depending on the distance offshore.
The closest public courses are the Hammock Bay Golf and Country Club, 1370 Borghese Lane (tel. 239/259-1100; www.hammockbaygcc.com), located on the pristine track of land that was known for years as Marco Shores Golf Club. The course was totally redesigned and crafted by Peter Jacobsen, and Marriott's Golf Club at Marco (tel. 239/353-7061), both in the marshlands off Fla. 951 north of the island. A sign at the Marriott's course ominously warns: PLEASE DON'T DISTURB THE ALLIGATORS. Fees range from as much as $200 in winter down to $75 in summer.
Beaches -- The sugar-white Crescent Beach curves for 3 1/2 miles down the entire western shore of Marco Island. Its southern 2 miles are fronted by an unending row of high-rise condominiums and hotels, but the northern 1 1/2 miles are preserved in Tigertail Public Beach (tel. 239/642-8414), at the end of Hernando Drive. Restrooms, cold-water outdoor showers, a children's playground, watersports rentals, and a snack bar are available here. The park is open daily from dawn to dusk. There's no admission charge for the beach, but parking in the lot costs $3 per vehicle. The beaches in front of the Marriott, Hilton, and Radisson resorts have parasailing, windsurfing, and other watersports activities, all for a fee.
If you're not staying at the big resorts, Collier County maintains a $3-per-vehicle parking lot and access to the developed beach on the southern end of the island, on Swallow Avenue at South Collier Boulevard.