You would not be able to start above strontia currently.
Lower waterton canyon is currently closed to all.
Waterton Canyon Closure FAQs | Denver Water
Even when it reopens, Lower waterton is closed to boating, and strontia is always closed to boating, so that means one hell of a portage.
You could normally start at Chatfield, but there is also a closure on the urban Platte from approx 8th ave to 15th ave. In any case there is not really enough water to float this time of year anyway. You could probably pull off Chatfield to Evans next spring...Have fun!