The Saint Marks River is a 36-mile-long, spring-fed tidal river flowing south through Florida's Big Bend region into Apalachee Bay. For paddlers, it offers a mix of protected, scenic stretches and open, tidal waters. The river is characterized by clear, spring-fed sections, overhanging vegetation, and a generally flat, undeveloped shoreline that provides a tranquil, natural setting. A notable geographical feature is a natural bridge where the river disappears underground for a stretch, and it is fed by a first-magnitude spring known as the St. Marks River Rise.

Several access points facilitate paddling trips. Shields Marina, located on Riverside Drive in St. Marks, offers a double boat launch with all-tide access, convenient for kayaks and paddleboards. The Saint Marks River Preserve State Park also provides a boat launch. For hand-launched craft like kayaks and canoes, a ramp on the East River Pool within the Saint Marks National Wildlife Refuge drains into the Saint Marks River. The southern terminus of the Tallahassee-St. Marks Historic Railroad State Trail has a small parking area right across from the trailhead on the river, though parking is not allowed at night. Paddlers should be aware that the river features deep tidal waters, and the old railroad bridge no longer exists, making direct crossing impossible for long-distance hikers on the Florida Trail, a situation that highlights the river's significant tidal influence.

The area is rich in wildlife, with opportunities to see turtles, herons, ducks, osprey, eagles, otters, alligators, and manatees. The surrounding ecosystems include pine flatwoods, scrub, and hardwood hammocks, supporting species like the gopher tortoise and Florida black bear. For amenities, the riverside community of St. Marks offers restaurants like the Riverside Café, which is located directly on the water. Kayak, canoe, and SUP rentals are available from local businesses such as St. Marks Outfitters and T-n-T Hideaway Rental. The best seasons for visiting are fall and winter, and crowd levels are typically low. The river's proximity to the St. Marks National Wildlife Refuge and the paved Tallahassee-St. Marks Historic State Trail adds to the recreational options in the area.