Little bluestem blue heaven is dying
Greetings! Thank you for contacting AaE for help.
I can't tell much from the photos of the plants themselves. Little bluestem grass is usually problem free as long as it is grown in conditions that are good for it and most conditions are good for it.
Do you know of any recent herbicide spraying done in the vicinity? If the wind drifts the chemicals toward your plantings, you'll see curling, browning and cupping of leaves on the side closest to the spray. Your photos don't show the entire area of plantings so I can't tell if just one side is affected but you can certainly ascertain that.
Another problem is if its roots are consistently wet then the plant's roots will rot and the plant will show signs of decline. I see that they are close to the shoreline and, yes, some of the grass plants appear to be right next to the water and seem fine but a check of that area may reveal that the water drains out of that area better than where the dying ones are. Pull up one of the affected plants and look at the roots to see if they are rotting or not.
Finally, if you think they are affected by a fungus, you could send a living but affected section of the plant to the U of MN Extension Plant Disease Clinic for a diagnosis. I'm including a link to their web page where you can learn more about their services, prices and how to submit a sample.
I hope this information helps.