I came across a situation today that I couldn’t figure out. I was fishing on the Mohawk River in NY and there were literally miles of emergent weeds (in this case water chestnut). I know to look for irregularities like downed limbs, random pockets, etc., but what other factors come into play when you’re dealing with such a vast area to break down?

If you can, cruise through and check for depth changes, or other bottom irregularities. You could spend a lot of time casting in an area like this.

Something different, could be one or more of several things. 

Bottom changes. If you can look ahead of time on navionics you can find points or breaks. If it’s a place you fish often and know the weeds will be there yearly, go in early spring and graph the area. 
 

the other thing to figure out is if they are up high, mid column, or down low in the weeds. Not much sense dragging a Texas rig across the points if the fish are shallow and looking up. 

Current and anything that changes or alters current flow including the vegetation edges.

Flip and pitch around where it makes pockets and points.

or punch a bait thru to see if anyone is home at the bottom?

It's like fishing the shady side VS fishing the sunny side

On the shady side every piece of anything is in the shade

hard to focus anywhere.

 

But on the sunny side is where you will find isolated pieces of cover/structure that will be shaded

these give precise targets

Just spit ball'n here

 

If it transitions to another type veg, that could be spot to work. Also check to see if rock/boulders are adjacent. Usually that transition is productive.

 

Veg Humps and depressions are usually money.

As noted above current (moving water) and structure are your primary factors, not the cover.

Trout anglers are good at reading moving water and know what creates eddies and seems that create current breaks.

Smallmouth bass in current are very similar to trout in this regard, they both face into the current direction waiting for prey to come to them. The fish hold where the faster moving water comes against slower moving creating a seem with slower current. Structure like boulders, jetties/wing dams, trees, channel bends, shallower water flowing into slower deeper water etc.

Now add cover to the above elements.

Tom

2 hours ago, Jigfishn10 said:

If it transitions to another type veg, that could be spot to work. Also check to see if rock/boulders are adjacent. Usually that transition is productive.

This has been my experience. Finding places where the vegetation changes or is mixed together. Anything different is usually something that will hold fish. Different vegetation, depth, current, wood/rocks mixed in, mats on the surface, etc. 

Miles of weedbeds = miles of topwater