The Lamar River is a significant tributary of the Yellowstone River, flowing entirely within Yellowstone National Park in northwestern Wyoming. Originating in the Absaroka Range, the river flows northwestward for approximately 40 miles (64 km) before joining the Yellowstone River. The Lamar River drains a watershed of about 668 square miles (1,730 km��), making it the largest tributary to the Yellowstone River within the park boundaries. While the Lamar River itself is not typically used for paddling, it is renowned for its scenic beauty and exceptional fly fishing opportunities.

The river flows through the expansive Lamar Valley, often called America's Serengeti due to its abundant wildlife. The primary way to experience the Lamar River is via the Lamar River Trail, a 33-mile (53 km) hiking path that follows the eastern bank of the river. This trail offers relatively easy hiking with minimal elevation change, making it suitable for day hikes and multi-day backpacking trips. The trail begins at the Soda Butte / Lamar River Trailhead and extends to Cold Creek.

The best time to visit the Lamar River area is from late spring through early fall, typically June through September, when the weather is most favorable and wildlife viewing opportunities are at their peak. Winter access is limited due to road closures and harsh conditions.

The Lamar Valley is famous for its diverse wildlife, including large herds of bison, elk, and pronghorn antelope. It's also one of the best places in Yellowstone to spot wolves and grizzly bears. The river and surrounding meadows support a rich ecosystem of plants and animals, including various wildflower species in spring and summer.

Key points of interest along the river include the historic Lamar Buffalo Ranch, established in 1907 to help preserve the American bison, and the Lamar Valley itself, known for its sweeping vistas and wildlife viewing opportunities.

Access to the Lamar River area is primarily via the Northeast Entrance Road in Yellowstone National Park. The nearest towns are Cooke City and Silver Gate, Montana, just outside the park's northeast entrance. Visitors should be aware of park regulations, including proper food storage and maintaining safe distances from wildlife (at least 100 yards from bears and wolves). The area is in prime grizzly bear habitat, so carrying bear spray and knowing how to use it is essential.

For those interested in multi-day trips, backcountry camping is available along the Lamar River Trail with proper permits from the National Park Service. These trips offer unparalleled opportunities to immerse oneself in the pristine wilderness and potentially observe wildlife away from the more crowded roadside areas.