That's Northern Milfoil...Coontail looks like this

I mean, if you zooms in, they look really similar ? How do you  tell them apart ,

The short-stubby branches off the main run are indicative of milfoil. Coontail has longer, more 'whispy' branches.

Another shot of coontail.

16 minutes ago, MN Fisher said:

The short-stubby branches off the main run are indicative of milfoil. Coontail has longer, more 'whispy' branches.

Another shot of coontail.

You’re right 

2 minutes ago, Bandersnatch said:

You’re right 

Hope so - a section of one of my classes in college was running down the taxonomic tables to identify water plants...my major was Aquatic Biology.

Another ‘milfoil’ vote. 
 

Milfoil is often like a handful of wet noodles when lifted out of the water. Coontail stems and leaves hold their shape and stiffness much better.

 

The softer reddish stem of milfoil is sometimes a giveaway. Also, the “leaves” actually look like leaves or even feathers, with a central vein/stem and lots of fronds branching off that, versus more just a central clump of fronds, often splitting into double fronds like a wishbone. 

That's a milfoil !!

That's milfoil.  The end of coontail, looks like a raccoon's tail.