The Gardner River, also known as the Gardiner River, is a significant tributary of the Yellowstone River in northwestern Wyoming and south central Montana. Originating on Joseph Peak in Wyoming, the river flows northward for approximately 25 miles before joining the Yellowstone River near the town of Gardiner, Montana, at the northern boundary of Yellowstone National Park. The river offers diverse paddling opportunities, ranging from calm scenic floats to exhilarating whitewater runs.

The most popular section for whitewater enthusiasts is the 8-mile Town Stretch from Gardiner to Miner, Montana, featuring Class II-III rapids. This family-friendly section typically takes 2.5 to 3 hours to complete and offers stunning views of Mount Sepulcher and Electric Peak. For more experienced paddlers, the Yankee Jim Canyon section downstream provides a challenging Class III-IV whitewater experience. This 5-mile stretch runs from Joe Brown to the Carbella bridge and is typically only navigable for a couple of months each year due to water levels. The river's difficulty ranges from Class I-II in its calmer sections to Class III-IV in Yankee Jim Canyon, accommodating beginners to advanced paddlers.

The best time for paddling is generally late spring through early fall, with peak flows occurring during spring snowmelt. The Gardner River valley is home to diverse wildlife, including elk, bighorn sheep, and various bird species. Paddlers may also spot thermal features along the river, most notably the Boiling River hot spring near Mammoth Hot Springs. Key landmarks include the confluence with the Yellowstone River, Boiling River hot spring, and the scenic vistas of Paradise Valley.

Primary access points are in Gardiner, Montana, with additional put-ins and take-outs at Joe Brown, Miner, and the Carbella bridge. Historically, the Gardner River played a role in early Yellowstone expeditions, including the Washburn-Langford-Doane Expedition of 1870. Today, it serves as a popular recreation area and a gateway to Yellowstone National Park.

Safety considerations include rapidly changing water levels, cold water temperatures, and the presence of thermal features. Paddlers should be aware of park regulations and obtain necessary permits when entering Yellowstone National Park. While most trips on the Gardner River are day excursions, multi-day adventures can be created by combining different sections or incorporating it into longer Yellowstone River trips. The river's proximity to Yellowstone National Park makes it an excellent addition to any park visit, offering a unique perspective on the region's natural beauty.