Fern Lake Trail, Historic hiking trail in Rocky Mountain National Park, Colorado, US.

Fern Lake Trail is a 4.8-mile (7.7 km) hiking trail in Rocky Mountain National Park, Colorado, running from Moraine Park west to Fern Lake. Its first stretch follows the Big Thompson River past The Pool, a wide spot in the river, and on toward Fern and Marguerite Falls. The route climbs to the lake at no more than a 10% grade, with Civilian Conservation Corps retaining walls along the way.

The trail began informally in the late 1880s as a route to The Pool, a wide spot on the Big Thompson River where a small lodge predated the park's 1915 establishment. The Estes Park Protective and Improvement Association improved it between 1907 and 1912, adding a bridge at The Pool, and two years later it was rebuilt to a maximum 10% grade for better access to Fern and Marguerite Falls. From 1933, Civilian Conservation Corps crews spent three years rebuilding it with retaining walls and a realigned path. It was listed on the National Register of Historic Places on February 28, 2005.

The trail's name comes from Fern Lake, its western terminus, and its first stretch follows the Big Thompson River to The Pool, where a small lodge stood before the park was created in 1915. Folksinger Judy Collins and her then-husband Peter Taylor ran Fern Lake Lodge in the summer of 1958, giving hikers a rest along the route.

Access via Bear Lake Road requires timed permits between May and October, so plan ahead. The parking area fills quickly, so arriving early makes sense.

The trail was listed on the National Register of Historic Places on February 28, 2005, recognized for its link to early tourism and its Civilian Conservation Corps construction. Look for the CCC-built retaining walls along the route.