The Nassau River is a coastal waterway in northeastern Florida, originating just west of Interstate 95 and flowing eastward to empty into the Atlantic Ocean at Nassau Sound. This tidal river forms part of the boundary between Duval and Nassau counties, winding through marshlands and coastal ecosystems as it approaches the sea.

Paddling on the Nassau River system is best experienced in its lower reaches and connected waterways near the coast. Simpson Creek, a major tributary, offers popular routes for kayakers and canoeists. The Northern Half Simpson Creek Trail begins at Kayak Amelia and travels 3.6 miles north to Nassau Sound, passing along the southeastern shore of Big Talbot Island State Park. The Southern Half Simpson Creek Trail covers the same distance heading south from Kayak Amelia to the confluence with Fort George River.

These paddling sections are rated as flatwater, suitable for novice paddlers. The waterways are tidal, with trips best timed to coincide with outgoing tides for easier paddling. Spring and fall offer ideal weather conditions, though summer paddles are popular for wildlife viewing.

The ecosystem supports a diverse array of flora and fauna. Paddlers may encounter dolphins, sharks, and various shorebirds, particularly at low tide when smaller fish concentrate in the channels. The shorelines feature oyster beds, marsh grasses, and coastal hammock vegetation.

Key landmarks include Big Talbot Island and Little Talbot Island State Parks, which preserve pristine barrier island habitats. Bird Island in Nassau Sound provides an important rookery. The Timucuan Ecological and Historic Preserve encompasses much of the area, protecting both natural and cultural resources.

Primary access points include Kayak Amelia on Simpson Creek and the Alimacani Ramp at Huguenot Memorial Park. These launch sites are located near Jacksonville, the largest nearby city.

The Nassau River and its surrounding areas hold significant historical importance, having been home to Native American tribes and later playing a role in early European settlement and maritime trade.

Paddlers should be aware of tidal fluctuations, which can dramatically affect water levels and currents. Weather conditions can change quickly in this coastal environment, so checking forecasts and being prepared for wind and potential thunderstorms is essential. While primarily suited for day trips, the network of waterways in the Nassau River system could potentially support multi-day adventures for experienced paddlers willing to carefully plan around tides and camping options in the state parks.