Shawn, Lake Bracciano is located about 50 miles north of Rome in a hilly volcanic area, the lake itself pretty much fills up a spent (are they ever) volcanic crater and the rim elevation goes to about 1200' within a couple of miles of the shore.
The NH90 performance took place after the National Aerobatic Team had completed their performance.
According to some witnesses the sky conditions and the lack of wind contributed to what is known as mirror effect on the water surface.
The a/c commander (Italian Army Captain) was supposedly highly experienced and was part of the development group for this type of a/c, he is survived by his wife and two daughters.