I live less than two miles from the Waterton Canyon trailhead, and wanted to add my two cents to the discussion, since there are some good questions floating around about this area. First, you will not like the fine if you bring any animal into Waterton Canyon. The Denver Water Company owns this area, and is strict about this rule. As you pass the trailhead sign, you pass the DWC operations center, with plenty of employees around. There is light but routine employee traffic on the 6 mile “water board road”, that serves as the first 6 miles of the CT. I would not risk it. Second, no public automobiles are allowed on the road, so there is no driving to Strontia Springs Dam. Now some good news - If you are not hung up on missing the 6 miles of dirt road with the multitude of mountain bikers (I’m not a mountainbiker, but rather a hiker and ultrarunner), you could always get dropped off at Roxborough State Park and take the Carpenter Peak trail about 3.25 miles until it connects with trail to Waterton Canyon. You will end up at the Strontia Springs dam, and will have avoided the 6 mile road hike. But, the 3 miles is a fairly decent climb to start with. Be aware that there is no camping in either Waterton Canyon or Roxborough State park.
Personally, I think the walk up Waterton Canyon next to the river is relaxing, if you go early in the morning. I run there most mornings. FYI
TrailGuy