Just getting into TR on my free month trial and starting with a Low Volume Olympic Tri program.
It doesn’t appear to relate any TSS to swims, however Elevate for Strava does allocate me a stress score based upon my CSS.
I assume I can manually enter that into the TR calendar for the swim sessions without it screwing any other measures up?
regards,
Greg
Yes you can. The swim stress will effect everyone differently. I add 20 TSS for each swim right now if for the only reason to make me feel good 
It is real stress, so you should add it.
Yep I track it to get a total TSS picture. I use the calculators from TP based off my CSS.
Check out this post and this thread in general. Swim TSS calculator linked.