There's only one island—called Fannette—in Lake Tahoe, and it rests in fjordlike Emerald Bay on the lake's California side. In winter, the bay and the state park on its shore have a "scrubbed-clean, crystal clear beauty," says Susan Grove, the area's park superintendent. Hike or snowshoe from a parking lot off Highway 89 down a steep trail of nearly a mile to Vikingsholm, a Scandinavian-style mansion built in 1929. You can tour the interior only in summer, but the mansion's grounds and bay views are accessible yearround. (530) 525-3345, parks.ca.gov/?page_id=506 .
The vivid blue waters of Bear Lake, on the edge of two adjacent state parks on the Utah-Idaho border, can be viewed from nearby snowmobile trails and mountain resorts. If the lake is frozen over, punch a hole in the ice to catch Bonneville cisco, a fish species found only here. (435) 946-3343, utah.com/stateparks/bear_lake.htm .
Coeur d'Alene Lake
As they do in Emerald Bay, divers troll for sunken boats in Coeur d'Alene Lake, off Highway 90 on the western edge of Idaho's panhandle. Other visitors head to the lake's Wolf Lodge Bay from late November to early January to watch migrating bald eagles feed on spawned-out salmon. (877) 782-9232, cdachamber.com 
Photography by Lee Foster /Lonely Planet
This article was first published in January 2010. Some facts may have aged gracelessly. Please call ahead to verify information.