The Canvasback reported in the Merrimack River at the Rocks Village Bridge today by the Buxtons was in nearly fresh or just slightly brackish water. Wild celery [Vallisneria americana] is commonly called freshwater eelgrass or water celery and is particularly favored by Canvasbacks [Aythya valisineria]. I've seen water celery in that area of the river while kayaking there. Canvasbacks will also eat mollusks, aquatic insects and some small fish.
Male Canvasback by Jeremiah Trimble
On Saturday, I searched this freshwater area of the river for the Canvasback after seeing the 1/24 report that Steve Mesick saw a Canvasback in Newburyport harbor.