Dog Lake is often accessed from Millcreek Canyon, but you can also get to it from Big Cottonwood by way of Mill D North. There is a lot going on nearby when it comes to outdoor activity in the winter. It is located across the street from the Donut Falls Trail and sledding hill, and it has the same trailhead as Reynolds Gulch. The journey to Dog Lake is 2.6 miles one way, but remember that if you want to bring your dog to their namesake watering hole, you would need to come up the Millcreek way.
Heading north on the trail from the parking lot there is a fork a short way up, and you'll want to stay to the right. The trail is steep at first, but it levels out to a relatively flat hike by Wasatch mountain standards. The snow is usually packed down because it's a popular trek. Beautiful aspen groves line the trail and there are heavy pine forests at the start, but the trail opens up further into the canyon. There is another fork in the trail about 2 miles up: left is Dog Lake, and right is Lake Desolation.
Along the hike you will see endless backcountry ski tracks coming down from all sides. You get great views of Kessler Peak and Mount Superior, Reed and Benson Ridge, Silver Fork Ridge, Mount Raymond, and Little Water Peak. It's a really pretty trail in winter, and it's not too difficult. As you approach Dog Lake, the pitch increases steadily while passing over the saddle. Just on the other side you reach the snow-covered lake. When you arrive, consider taking the quick route up to the left just a few hundred feet to the top of the hill. There are some nice vistas from up there that you just don't get if you stay down by the lake.
There are a few spots that could be terrain traps for avalanches, but the surrounding valley walls aren't very steep other than a few places. Always check the conditions at the Utah Avalanche Center before you head up, and remember there are no 100% safe days out there in winter, so be smart and prepared!
Winter backcountry adventures can be dangerous outdoor activities that pose significant risks as conditions affecting safety (i.e. weather, snowpack stability, avalanche hazard) are constantly changing. Prior to engaging in these activities each individual should get the proper training to make safe decisions and be equipped to use avalanche safety resources and tools. Please visit our Backcountry Skiing and Avalanche Safety post to learn more.