Round trip distance: 6 miles
Highest point: 3,800 feet
Elevation gain: 700 feet
WTA page: http://www.wta.org/go-hiking/hikes/source-lake
Source Lake shares a trail with the super popular Snow Lake trail. I'm not a fan of crowded trails, so I didn't enjoy the first 2/3rds of the hike. However, once we got to where the Source Lake trail split off from the Snow Lake trail, it was much quieter and more peaceful (a fellow hiker said to us as we passed by "you chose the quiet trail"). We only saw 5 or 6 other people.
Once the trail splits off, it's not very far to get to a viewpoint for the lake. It would be easy to visit Source Lake and then continue on to Snow Lake.
We didn't go down to the lake, but it is an option. Source Lake is tiny but there are nice views of the surrounding mountains and the small valley that Source Lake lies in. It's a good place to sit and enjoy the scenery and have a snack.
When we hiked, it was hazy from the ongoing wildfire smoke from other areas of Washington.
I'd recommend this hike if you want something easier without a lot of elevation gain and if you'd rather take a quieter trail (instead of continuing to Snow Lake).