Thank you for writing.

When it is mown and the tops are cut off, I can't tell

It could be nimble will https://turf.purdue.edu/nimblewill/

Long stick sedge   https://www.minnesotawildflowers.info/grass-sedge-rush/long-stalked-sedge

Orchard Grass https://turf.purdue.edu/orchardgrass/

Tall Fescue is also possible https://turf.purdue.edu/tall-fescue/

and possibly Lily Turf

I am sorry to not be of more help. There is no way to tell when it is mowed like this.

Lou 

Thank you for writing back.

Sorry to be late writing back. I was in Chicago. 

That is a great question.  Lawn monocultures are inherently non-sustainable because of changes in sun shade, wet dry, soil compaction creates subzones in your lawn that offer different competitive advantages to different plants. http://ci.chanhassen.mn.us/DocumentCenter/View/4789/Choosing-Lawn-Grasses-UMN-Extension?bidId=

Also the blues are very high maintenance in terms of water and soil conditions.  Blues do best in a fair amount of water (not so this year) and if allowed to grow deep roots by mowing them at 3.5-4 inches.  Basically, the taller the grass the deeper the root and the stronger the plants and the less susceptible the turf is to invasions.
Many urban lawns are compacted and core aeration done about now can reap big dividends.https://extension.umn.edu/lawn-care/renovating-lawn-quality-and-sustainability

Many lawns are way over fertilized.  Fertilizing is non-selective growing non-desirables as much as desirables and also nitrogen burn is a big problem adversely affecting lawns /https://homeguides.sfgate.com/save-nitrogen-burned-lawn-76736.html

The selectivity of herbicides is dose dependent.  So if runoff or uneven application is carrying herbicides to some area, they can affect a bluegrass.

All this is a way of saying that I know nothing about your lawn but it is probably better to think of tall fescue is a symptom of an environment which is become less well suited to blues AND that pure blues are a difficult choice.  There are other options. Blue 50/fine fescue 45/dutch white clover 5% for pollinators and to add nitrogen to soil is one possibility.  Bee lawns are another.
But for this year, core aeration, rake, overseed with blue /fine fescue (you can see this at the fair near the Energy Building). Do not mow this year so you do not pull the new seedlings out.

Best